Bukhari

And Allah the Exalted has said: «لا يحب الله الجهر بالسوء من القول إلا من ظلم وكان الله سميعا عليما‏» "Allah does not like the public mention of evil except by one who has been wronged, and Allah is Hearing and Knowing." (And the statement of Allah:) «والذين إذا أصابهم البغى هم ينتصرون‏» "And those who, when tyranny strikes them, they defend themselves." Ibrahim said that the Salaf did not like to be humiliated, but when they gained power over (the oppressor), they would forgive him.

And Allah the Exalted has said that «إن تبدوا خيرا أو تخفوه أو تعفوا عن سوء فإن الله كان عفوا قديرا‏» "If you do good openly or secretly, or pardon someone for a bad matter, then Allah is Most Forgiving, Most Powerful." (It is stated in Surah Ash-Shura) «وجزاء سيئة مثلها فمن عفا وأصلح فأجره على الله إنه لا يحب الظالمين * ولمن انتصر بعد ظلمه فأولئك ما عليهم من سبيل * إنما السبيل على الذين يظلمون الناس ويبغون في الأرض بغير الحق أولئك لهم عذاب أليم * ولمن صبر وغفر إن ذلك لمن عزم الأمور‏ ، وترى الظالمين لما رأوا العذاب يقولون هل إلى مرد من سبيل» "And the recompense of an evil is an evil like it, but whoever forgives and makes reconciliation, his reward is with Allah. Surely, Allah does not like the wrongdoers. And whoever takes retribution after being wronged, there is no blame upon them. The blame is only upon those who wrong people and commit oppression upon the earth without right; for them there will be a painful punishment. But whoever is patient and forgives, indeed, that is of the matters requiring determination. And O Prophet! You will see the wrongdoers, when they see the punishment, saying, 'Is there any way to return to the world?'"

Narrated Ibn `Umar: The Prophet said, "Oppression will be a darkness on the Day of Resurrection."