Mujahid says: I heard Ibn Abbas (may Allah be pleased with them) saying that retribution (qisas) was obligatory upon the Children of Israel and there was no blood money (diyah) among them. So Allah Almighty prescribed this ruling for this Ummah: "Retribution for the slain has been made obligatory upon you: the free for the free, the slave for the slave, the woman for the woman. But if any remission is made to one by his brother, then let there be a suitable follow-up and payment to him with good conduct. This is a concession and mercy from your Lord." This is in contrast to what was made obligatory upon those before you. "But whoever transgresses after that will have a painful punishment." (__QUR_N__ al-Baqarah: 178)
Hadith Referenceمسند الإمام الشافعي / كتاب القتل والقصاص والديات والقسامة / 1635
Hadith Takhrijاخرجه البخاري، التفسير ، باب ﴿يايها الذين امنوا كتب عليكم القصاص﴾ (4498)۔