Injustice is deviation from justice and violation of the truth.
There are three broad types of injustice:
1-   To be unjust towards Allah The Almighty: The most heinous forms of this type are disbelief, polytheism, and hypocrisy. Allah The Almighty Says (what means):  
{And [mention, O Muhammad], when Luqmaan said to his son while he was instructing him, “O my son, do not associate [anything] with Allah. Indeed, association [with him] is great injustice.”}[Qur’an 31:13] 
{Indeed, the curse of Allah is upon the unjust.} [Qur’an 11:18]
2-   To be unjust towards other people: Allah The Almighty Says (what means): 
{And the recompense of an odious deed is an odious deed the like of it; yet whoever is clement and acts righteously, then his reward is up to Allah. Surely, He does not love the unjust.}[Qur’an 42:40] 
{The cause is only against the ones who wrong the people and tyrannise upon the earth without right. Those will have a painful punishment.} [Qur’an 42:42] 
3-   To be unjust towards oneself: Allah The Almighty Says (what means):
{Then we caused to inherit the Book those We have chosen of Our servants; and among them is he who wrongs himself.} [Qur’an 35:32] 
{He [Moosa] said, “My Lord, indeed I have wronged myself, so forgive me,” and He forgave him. Indeed, He is the Forgiving, the Merciful.} [Qur’an 28:16] 
In fact, all three types are considered as doing injustice to oneself as one wrongs oneself when one intends to do injustice.
Ath-Thahabi, may Allah have mercy upon him, maintained that injustice is a major sin and said that doing injustice to others may take the form of trespassing on their property, abusing them physically or verbally, and attacking the weak. He mentioned the Qur’anic verses and Prophetic Hadiths that threaten the unjust. Then he reported that some of the righteous predecessors said, “Do not wrong the weak so as not to be one of the evil strong people.” In addition to this, he mentioned some forms of injustice that he considered to be major sins: 
* Devouring the property of orphans  
* Procrastination in repaying debts despite the ability to repay at the due time.
* Denying a wife her rights such as dowry, clothing and provision.
* Denying a labourer his wage or salary   
* Inaccurate divisions and valuation, which are considered major sins, according to Ibn Hajar, may Allah have mercy upon him.

The Texts of the Shari‘ah Dispraise Injustice

Allah The Almighty Says (what means):  
{And those cities - We destroyed them when they wronged, and We made for their destruction an appointed time.} [Qur’an 18:59] 
{And in no way did We do injustice to them, but it is they who were the unjust.} [Qur’an 43:76] 
{Allah does not love the unjust.}[Qur’an 3:57] 
{And your Lord does injustice to no one.}[Qur’an 18:49] 
{And your Lord is not ever unjust to [His] servants.} [Qur’an 41:46] 
{Verily the unjust are surely in perpetual torment.} [Qur’an 42:45]  
In addition, there are many Qur’anic verses that speak about doing injustice to oneself. These verses explain that this type of injustice comes in two forms: Shirk (polytheism), and disobeying Allah The Almighty. Shirk is the most heinous of sins; Allah The Almighty Says (what means): {Then we caused to inherit the Book those We have chosen of Our servants; and among them is he who wrongs himself, and among them is he who is moderate, and among them is he who is foremost in good deeds by permission of Allah. That [inheritance] is what is the great bounty.}[Qur’an 35:32]  
Doing injustice to others through aggression against their lives, property or anything else, is dispraised in many Qur’anic verses such as the verse that reads (what means):{The cause is only against the ones who wrong the people and tyrannise upon the earth without right. Those will have a painful punishment.}[Qur’an 42:42] 
Similarly, the Hadiths of the Prophet, sallallaahu ‘alaihi wa sallam, dispraise injustice:
* It was narrated on the authority of Abu Moosa Al-Ash‘ari, may Allah be pleased with him, that the Prophet, sallallaahu ‘alaihi wa sallam, said: “Indeed, Allah gives respite to the oppressor, but when He seizes him, He does not let him escape.” Then he recited:{And thus is the taking away of your Lord when He takes away the towns [while] they are unjust; surely His taking away is painful [and] strict.}[Qur’an 11:102] [Al-Bukhari and Muslim] 
* The Prophet, sallallaahu ‘alaihi wa sallam, said:“Protect yourselves against doing injustice, for injustice will be darkness on the Day of Resurrection.” [Muslim]
* ‘Aa’ishah, may Allah be pleased with her, said to Abu Salamah ibn ‘Abdur Rahman, may Allah be pleased with him, who was disputing with some people over a piece of land, “O Abu Salamah, beware of seizing land unjustly because the Prophet, sallallaahu ‘alaihi wa sallam, said, ‘Whoever seizes unlawfully a hand-span of land, a collar of seven lands will be around his neck [in the Hereafter].’” [Al-Bukhari and Muslim] 
* It was narrated on the authority of Huthayfah, may Allah be pleased with him, that the Prophet, sallallaahu ‘alaihi wa sallam, said: “Do not be blind followers and say: ‘If people do good, we do good, and if people do injustice, we do injustice.’ Adjust yourselves; when people do good, do good, and when they wrong, do not do injustice.”[At-Tirmithi] 
* It was narrated on the authority of ‘Abdullah ibn Mas‘ood, may Allah be pleased with him, that the Prophet, sallallaahu ‘alaihi wa sallam, said: “Whenever a person is murdered, there is a share of the burden of the crime on the son of ’Aadam [Adam], may Allah exalt his mention, since he was the first to commit murder.”[Al-Bukhaari and Muslim] 
* It was narrated on the authority of Abu Hurairah, may Allah be pleased with him, that the Prophet, sallallaahu ‘alaihi wa sallam, said: 
Do not envy one another; do not commit Najash [to overbid against a rival purchaser simply to harm him with no intention of buying the merchandise]; do not hate one another; do not turn your backs on one another; do not enter into commercial transactions when others have entered into that [transaction]; rather, be, O slaves of Allah, brothers. A Muslim is the brother of a Muslim; he does not do injustice to him, he does not let him down, and he does not disdain him. Piety is here, [and he pointed to his chest three times]. It is enough evil for a Muslim to disdain his brother Muslim. All of a Muslim is inviolable for other Muslims: his blood [life], his property and his honour.[Muslim] 
The righteous predecessors also dispraised injustice in their sayings:
*  ‘Ali ibn Abi Taalib, may Allah be pleased with him, said, “The day when the wronged will triumph over the wrongdoer will be far severer than the day when the wrongdoer wronged him.” Mu‘aawiyah, may Allah be pleased with him, would say, “I would be terrified to wrong a person who has none but Allah The Exalted to seek His help against me.”
* Abu Al-‘Aynaa’, may Allah have mercy upon him, said, “I had some unjust enemies, and I complained about them to Ahmad ibn Abi Daawood. I said to him, ‘They have become united like a single hand against me!’ He replied, ‘{The hand of Allah is over their hands.}[Qur’an 48:10]’ I said, ‘They are cunning!’ He replied, ‘{The evil plot does not encompass except its own people.} [Qur’an 35:43]’ I said, ‘They belong to a large company.’ He replied, ‘{How many a small company has overcome a large company by permission of Allah The Exalted.}[Qur’an 2:249]’”.
* Yoosuf ibn ’Asbaat, may Allah have mercy upon him, said, “Whoever wishes an oppressor long life wants Allah The Exalted to be disobeyed in His universe.” 
* Ibn Mas‘ood, may Allah be pleased with him, said, “When the punishment was removed from the people of Yoonus, may Allah exalt his mention, they all returned the rights of others to the extent that a man would pluck a stone out of the foundation of his house and return it to its owner.”
* Abu Thawr ibn Yazeed, may Allah have mercy upon him, said, “Using an unlawfully acquired stone in a building is considered the beginning of its destruction.”
* A scholar said, “Had a single stone of injustice been used in building Paradise, the House of Eternity, it would have been ruined.”
* A sage said, “When you want to do injustice, remember the justice of Allah The Almighty that will be executed against you. When you want to use your strength to wrong others, remember that Allah The Exalted has the strength to punish you. Never, be impressed by someone who sheds blood, as his Assassin never dies.”
* Yazeed ibn Haatim would say, “I fear nothing more than a person whom I wronged while knowing that he has no supporter but Allah The Exalted, especially when he says, ‘Allah The Exalted is sufficient to judge between me and you.’”
* One day, ‘Ali ibn Al-Fudhayl wept, so he was asked why. He replied, “I feel sorry for those who wronged me, because they will have nothing to say to Allah The Almighty as an excuse.”
* While Sulaymaan ibn ‘Abdul-Malik was on the pulpit, a man said to him, “Remember the Day of Announcement!” Sulaymaan descended from the pulpit and asked the man, “And what is the Day of Announcement?” The man answered, “Allah The Almighty Says (what means): {Then an announcer will announce between them, “The curse of Allah be on the unjust.”}[Qur’an 7:44]”
* Abu Ad-Dardaa’, may Allah be pleased with him, said, “Beware of the orphan’s tears and the supplication of a wronged person.”
* Some scholars state that there are three types of injustice: 
*  Unforgivable injustice: This type refers to Shirk, from which we seek refuge with Allah The Exalted. Allah The Almighty Says (what means): {Indeed, Allah does not forgive association with Him, but He forgives what is less than that for whom He wills.}[Qur’an 4:48] 
*  Injustice that cannot be waived: This type refers to doing injustice to the servants of Allah The Almighty.
*    Forgivable Injustice: This type refers to wronging oneself.
* A man passed by a person whom Al-Hajjaaj had crucified, and said, “O Allah, your leniency with the oppressors has harmed the oppressed.” When the man slept that night he saw in a vision that he entered Paradise, and saw the man who had been crucified in the highest ranks of Paradise; then he heard a caller say, “My leniency with the oppressors has admitted the oppressed people to the highest ranks in Paradise.”
* It was said, “Whoever plunders others property, others will plunder his property.”  
*  It is said, “Whoever does injustice for long, loses power.”
* ‘Umar, may Allah be pleased with him, said, “Beware of the supplication of an oppressed man, as it is answered.”
* ‘Ali, may Allah be pleased with him, said, “The previous nations were destroyed because they kept denying people’s rights until this became rampant, and they spread transgression until its rights were ransomed.” 
* It was said, “The most evil of all wrongdoers is the one who wrongs some people for the benefit of others.”  
* Ibn Al-Jawzi said, “Injustice necessitates two sins: usurping others’ rights and defying Allah The Exalted with disobedience. The sin of doing injustice is more evil than other sins because it is usually committed against the weak, who are powerless to fend for themselves. The cause of injustice is the darkness of the heart; a man whose heart is lit with guidance would not commit injustice.”
* Ibn Taymiyyah, may Allah have mercy upon him, said, “People unanimously agree that the consequences of injustice are dire and that the outcomes of justice are good.” He also said that, “Allah The Exalted grants victory to a just state even if it is a non-Islamic state, and lets an unjust state be defeated, even if it is an Islamic state.”

Causes of Injustice
A- The devil: Allah The Almighty Says (what means):
 {O you who have believed, enter into Islam completely [and perfectly] and do not follow the footsteps of Satan. Indeed, he is to you a clear enemy.} [Qur’an 2:208] 
{Satan has overcome them and made them forget the remembrance of Allah. Those are the party of Satan. Unquestionably, the party of Satan - they will be the losers.} [Qur’an 58:19]
B- A persistent evil-enjoining soul; Allah The Almighty Says (what means):{Indeed, the soul is a persistent enjoiner of evil.}[Qur’an 12:53]
C- Personal inclination; Allah The Almighty Says (what means):
{So follow not [personal] inclination, lest you not be just.} [Qur’an 4:135]
{But as for he who feared the position of his Lord and prevented the soul from [unlawful] inclination, then indeed, Paradise will be [his] refuge.}[Qur’an 79:40, 41] 
{…and do not obey one whose heart We have made heedless of Our remembrance and who follows his desire.} [Qur’an 18:28] There many other similar verses.

Curing and Giving Up Injustice

1-   Remembering that Allah The Almighty never does injustice; He Says (what means):
{Whoever does righteousness - it is for his [own] soul; and whoever does evil [does so] against it. And your Lord is not ever unjust to [His] servants.}[Qur’an 41:46]
{Indeed, Allah does not do injustice, [even] as much as an atom’s weight}[Qur’an 4:40]
{Allah wants no injustice to the worlds.} [Qur’an 3:108]
2-   Considering the fateful destiny of unjust people: Allah The Almighty Says (what means):
{And decidedly not one of you [there is], except that he will go [herded] down to it; that, for your Lord, has been a thing decreed, a must. Thereafter, We will safely deliver the ones who were pious and leave behind the unjust [ones], [abjectly] kneeling.} [Qur’an 19:71, 72]
{And your Lord would not have destroyed the cities unjustly while their people were reformers.} [Qur’an 11:117]
{Say, “Have you seen for yourselves? In case the torment of Allah comes up to you suddenly or openly, will any be perished except the unjust people?”} [Qur’an 6:47]
3-   Not to despair of the Mercy of Allah The Almighty: He Says (what means): {Indeed, no one despairs of relief from Allah except the disbelieving people.} [Qur’an 12:87]. It was narrated on the authority of Safwaan ibn Muhriz that a man asked Ibn Umar, may Allah be pleased with him, “What did you hear the Messenger of Allah, sallallaahu ‘alaihi wa sallam, say in private?” Ibn ‘Umar replied, “I heard the Prophet, sallallaahu ‘alaihi wa sallam, say:
A believer will be brought extremely close to his Lord on the Day of Resurrection. Enveloping him in His Mercy; He will make him confess to his sins by asking him: “Do you remember doing this sin and that sin?” He will reply: “Yes, my Lord, I remember.” Then Allah The Almighty will Say, “I covered it up for you in the worldly life, and I forgive you for it today.” Then the record of his good deeds will be handed to him. As for the disbelievers and hypocrites, their evil acts will be exposed publicly {…and the witnesses will say, “These are the ones who lied against their Lord.” Unquestionably, the curse of Allah is upon the wrongdoers...} [Qur’an 11:18]”[Muslim]
Moreover, the Hadith about the story of the man who killed ninety-nine people, as well as the one who said: “By Allah, if my Lord takes hold of me, He would torment me as He has not tormented anyone else.” [Al-Bukhari and Muslim], support the same meaning that a believer must not despair of the mercy of Allah The Almighty.
4-   Imagining the predicament of reckoning and judgment on the Day of Judgment; Allah The Almighty Says (what means): {And the earth will shine with the light of its Lord, and the record [of deeds] will be placed, and the prophets and the witnesses will be brought, and it will be judged between them in truth, and they will not be wronged. And every soul will be fully compensated [for] what it did; and He is most knowing of what they do.}[Qur’an 39:68-70]
5-   Remembrance and mentioning of Allah The Almighty and seeking His forgiveness: Allah The Almighty Says (what means): {And those who, when they commit an immorality or wrong themselves [by transgression], remember Allah and seek forgiveness for their sins - and who can forgive sins except Allah? - and [who] do not persist in what they have done while they know.} [Qur’an 3:135]
6-   Restraining oneself from doing injustice and returning rights to their owners: Sincere repentance is to feel remorse in the heart, to restrain oneself from disobeying Allah The Exalted, to ask Him for forgiveness by the tongue, and endeavour to return rights to their owners. Consequently, whoever has transgressed against his brother’s honour, property or anything else, then let him ask for his forgiveness today before the time (the Day of Resurrection) when there will not be any dinars or dirhams and there will only good deeds and evil deeds, as mentioned in the authentic Hadith.

Consequences and 
Harms of Injustice
* Injustice incurs the anger of Allah The Exalted.
* Allah The Almighty makes an unjust person suffer all types of torment.
* Injustice destroys families and states.
* An unjust person will be deprived of all forms of the intercession of the Prophet, sallallaahu ‘alaihi wa sallam.
* Letting unjust people go unpunished corrupts the entire Ummah (Nation) 
* Injustice is a sign of the hardness and darkness of the heart.
* An unjust person is low and mean in the sight of Allah The Exalted.
* Injustice causes one to lose the blessings of Allah The Almighty. The Qur’an tells us the story of the man who lost his two gardens because of his injustice: Allah The Almighty Says (what means):
{And he entered his garden while he was unjust to himself. He said, “I do not think that this will perish - ever. And I do not think the Hour will occur. And even if I should be brought back to my Lord, I will surely find better than this as a return.”} [Qur’an 18:35, 36]
 Injustice was the only cause of the destruction of previous kingdoms: {So the people that committed wrong were eliminated. And praise to Allah, Lord of the worlds.} [Qur’an 6:45]
{So We took him [Pharaoh] and his soldiers and threw them into the sea. So see how was the end of the wrongdoers.} [Qur’an 28: 40]
Allah The Almighty also tells us about the people of Lut (Lot), may Allah exalt his mention, Saying (What means): {So when Our command came, We made the highest part [of the city] its lowest and rained upon them stones of layered hard clay, [which were] marked from your Lord. And Allah’s punishment is not from the wrongdoers [very] far.}[Qur’an 11:82, 83]
Similarly, Allah The Exalted destroyed the people of Nooh (Noah), may Allah exalt his mention, Thamood, ‘Aad and the Companions of the Thicket. Allah The Almighty Says (what means): {So each We seized for his sin; and among them were those upon whom We sent a storm of stones, and among them were those who were seized by the blast [from the sky], and among them were those whom We caused the earth to swallow, and among them were those whom We drowned. And Allah would not have wronged them, but it was they who were wronging themselves.}[Qur’an 29:40]
The remorse of unjust people is useless if it comes too late; {And the Day that the unjust [person] will bite at both his hands, [and] say, “Oh, would that I had taken to myself a way along with the Messenger.”} [Qur’an 25:27] 
Injustice is one of the sins that cause one to be punished in this world and in the Hereafter because it affects others. This is no surprise, as the wronged person humbly and bitterly supplicates against the person who did injustice to him, and Allah The Exalted answers his supplication, Saying: “By My Might and Exaltedness, I shall rescue you, even if it be after some time.”
Hence, fear Allah The Almighty; be just and return the rights to whom they are due, before there comes a day when there will be no repelling.
Article source: http://www.islamweb.net/emainpage/