(O ye who believe! Retaliation is prescribed for you in the matter of the murdered…) [2:178].
Said al-Sha‘bi: “Fighting took place between two Arab tribes. One tribe had more power than the other and, therefore, they said: ‘For every slave of ours that you kill, we will kill a free man of yours, and for every woman of ours a man of yours’. And then this verse was revealed”.
Asbab Al-Nuzul by Al-Wahidi , trans. Mokrane Guezzou