Zayd bin Aslam (may Allah have mercy on him) said: In the Jahiliyyah, when a man of a tribe killed someone, (the slain man's people) would not be satisfied until they killed a noble man in his place; if the killer was not noble, they would not kill him but would kill someone else instead. So Allah Almighty revealed this verse as an admonition: "And do not kill the soul which Allah has made sacred, except by right. And whoever is killed unjustly, We have certainly given his heir authority, so let him not exceed limits in killing. Indeed, he has been supported." [Surah al-Isra': 33]. Zayd bin Aslam (may Allah have mercy on him) said: 'Israf fi al-qatl' (excess in killing) means that someone other than the killer should not be killed in his place. Imam al-Shafi'i (may Allah have mercy on him) said that Allah Almighty said: "Retaliation has been prescribed for you in the case of those killed." [Surah al-Baqarah: 178]
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنايات / 15889