Surah 16. An-Nahl, Ayah 126

Lit., "retaliate [or "respond"] with the like of what you have been afflicted with": thus, the believers are admonished to observe self-restraint while arguing with people of another persuasion, and never to offend against decency and intellectual equity. Although retaliation in argument is permissible if one's integrity is impeached by an opponent, the sequence makes it clear that it is morally preferable to renounce it altogether and to bear the unjust attack with patience.

In the context this passage refers to controversies and discussions, but the words are wide enough to cover all human struggles, disputes, and fights. In strictest equity you are not entitled to give a worse blow than is given to you. Lest you should think that such patience only gives an advantage to the adversary, you are told that the contrary is the case, the advantage is with the patient, the self-possessed, those who do not lose their temper or forget their own principles of conduct.