Hadith number 1279:
Narrated Ibn Umar: Allah's messenger salla allahu alayhe wasalam said: "Oppression will turn into darkness on the Day of Resurrection." (Agreed upon).

Hadith number 1280:
Narrated Jabir: Allah's Messenger salla allahu alayhe wasalam said: "Beware of oppression, for oppression will turn into excessive darkness on the Day of Resurrection; and beware of niggardliness, for niggardliness destroyed your predecessors." (Muslim)

Definition: The term "thulm" in Arabic means oppression. The Islamic definition of the word is manifold. They include:
a. transgressing the boundaries on oneself;
b. transgressing the boundaries of others;
c. claiming that which does not belong to oneself;
d. denying others their rights.

"Oppression will turn into darkness on the Day of Resurrection."

It is known in Islam that the punishment of a person in the Hereafter is similar to what he committed previously in the life of the Dunya. For instance, if a person has two wives and he mistreats one of them, then on the Day of Judgment he will come leaning on one side.

The Prophet (SalAllahu 'alaihi wassallam) states in these ahadith that oppression will turn into darkness on the Day of Resurrection. The reason for this is when someone oppresses another; he turns the life of another person into darkness. For instance, if one steals someone's $100 000, he changes that person's life into difficulties and gloominess. As a retaliation, on the Day of Judgment, Allah will darken the life of the oppressor for what he did.

Meaning of Darkness:
On the Day of Judgment, one will have to cross a bridge in order to gain entry into Paradise. The person's good deeds will act as a light so that he may cross and bridge and enter into Paradise. If someone oppresses, or is a disbeliever, a hypocrite, or a Muslim with very few good deeds, then they will not receive this necessary brightness to cross the bridge.

Oppression is a Major sin:
In the two hadith that are mentioned above, the Prophet (SalAllahu 'alaihi wassallam) compares oppression to darkness in the Life-after. This comparison implies that oppression is haram. It is not only haraam but it is worse than haram because it is clear in the sunnah whenever the Prophet (SalAllahu 'alaihi wassallam) specifies the punishment of an act, that sin is a major sin. If the Prophet (SalAllahu 'alaihi wassallam) does not mention the punishment of the sin, then it is categorized as a minor one. So this hadith proves that oppression is a major sin.

The reality of the Judgment Day:
This hadith is also a proof of the reality of Judgment Day. In Arabic, this is referred to as Yawm al-Qiyamah, or the 'day of standing'. Qiyamah literally means "to stand up" or "to prepare". There are three reasons why the Day of Judgment was given this name. First, we stand up to Allah on that day and are held accountable. Secondly, people will be brought to testify against each other and will get up on that day to do so. Finally, on that Day, the balance will be prepared to weigh the good deeds and the sins.

The hadith mentions the word taqwa, or fear. Although the word taqwa is usually understood to be the "Fear of Allah", this term has broad meaning. It includes not only fearing Allah, but also fearing Hell-fire, Day of Judgment, and oppression. Therefore, the hadith acts as an admonition against oppression, due to the seriousness of the sin.

"Beware of niggardliness"

Niggardliness is taking that which does not belong to oneself. This refers to material or physical objects. Consequently, niggardliness is a subcategory of oppression. This act was a reason for the nations before us to be destroyed. The Prophet (SalAllahu 'alaihi wassallam) is advising us to learn a lesson so that we will not be destroyed. Allah has promised not to annihilate the whole Muslim ummah, but rather a part of them if they transgress their boundaries. Allah says in the Quran "(The Muslim ummah) is the best nation created." Since this ummah was given many lessons from the past, as well as being the best nation created, if it transgresses the boundaries Allah has set, the punishment will be more severe.

There are many ahadith illustrating the seriousness and prohibition against oppressing others.

*In a hadith qudsi, Allah says, "Oh my servants, I prohibited oppression on myself, therefore don't commit oppression."

Allah, himself, does not oppress, but rather he chose to start with himself to show his servants the graveness of the matter.

*The Prophet (SalAllahu 'alaihi wassallam) said there was once a woman who oppressed a cat, and because of that, she was made to enter hell-fire. Conversely, there was a prostitute who was very thirsty. She saw a well and descended in order to fetch herself some water. On her way up, she noticed a thirsty dog. So she took her shoe and filled it up with water to give to the dog, so as not to oppress it. Because of her kindness, Allah granted her Paradise.

*The Prophet (SalAllahu 'alaihi wassallam) related there was a woman who was pious and a worshipper, but she oppressed her neighbors. She was doomed to Hell because of her oppressive behavior and actions.

Dua of the oppressed:
Allah promises to answer the dua of an oppressed person. The Prophet (SalAllahu 'alaihi wassallam) said: "Be afraid of the curse of an oppressed person as there is no screen between his invocation and Allah." (Al-Bukhari)

Allah gives an oath by His Majesty and Honor that anyone who is oppressed and invokes Him, He will grant him victory. There are three people who Allah will never reject their prayer. They are:
1) a just leader
2) a fasting person
3) someone who is oppressed

There lived a group of leaders in the Arabian Peninsula known as Barak. Though they were Muslims, they oppressed others and seized the wealth of people. The people living in the area continually made dua against the oppressive leaders. Eventually, the cruel leaders were apprehended. Once they were captured, one of the sons asked his father how they were able to be imprisoned. The father replied that it must have been by the prayer of someone who was oppressed, and therefore, Allah granted him his invocation.

Allah says in the Quran:
"When people forget and transgress their boundaries, we let them do what they want. When they feel proud that which they got, we take them swiftly, we annihilate the oppressors and praise be to Allah."

The Prophet (SalAllahu 'alaihi wassallam) said:
"There are two categories that I will not give intercession to on the Judgment Day. The leader who is oppressive and the other is one who is an extremist."

Types of Opression:

There are 2 types of oppression:
I. oppressing oneself
II. oppressing others

I. Oppressing oneself:

A person oppresses himself when:
1) he commits shirk. Allah says, "Shirk is the biggest of all oppression." Shirk is considered oppression for two reasons. First, because a person who associates with Allah, is doomed to hell. Secondly, one of the definitions of shirk is placing something where it doesn't belong. When a person commits shirk, he is essentially placing the worship of Allah where it doesn't belong. Worship is known only to Allah, and no other.

2) he commits sins. Allah says in the Quran: "Whoever transgresses the boundaries of Allah, he has oppressed himself."