AbuDharr reports Allah’s Messenger (peace and blessings of Allah be to him) as saying that Allah, the Exalted and Glorious, said: “My servants! I have made oppression unlawful for Me and unlawful for you; so do not commit oppression against one another.”
(Sahih Muslim)
Here the Messenger of Allah (peace and blessings of Allah be to him) who was sent to the world as Mercy to mankind, has forbidden the believers to commit oppression against one another. It is a hadīth-e-qudsi; so, though the narrator heard the Holy Messenger saying it but the words are those of Allah the Almighty. To commit oppression is such a heinous act that Allah, Who is Al-Rahman and Al-Raheem, first made it unlawful for His Exalted Self and then prohibited His servants from committing it. This enhances the height, seriousness and the exalted significance of the commandment.
The Arabic word zulm generally means: he did wrong or acted wrongfully, injuriously, or tyrannically. These English equivalents of the Arabic word are correct in their own ways, but in the Qur’ān the word al-zulm signifies the putting of a thing in a place not its own, or putting it in a wrong place, or misplacing it; it may also mean transgressing the proper limit.
Thus, the word zulm here implies that Allah does no wrong; whatever He does is based on justice; even when He punishes His servants He does what is good for them. So far as oppression on the part of human beings is concerned, it means commission of high-handedness against one another.