Musannaf Ibn Abi Shaybah 29818 — The blood of Muslims is of equal

Ibn Ashwa' said that al-Sha'bi said: There was fighting between two tribes of the Arabs. Some members of this tribe were killed, and some members of that tribe were also killed. One of these tribes said: We will not be satisfied until we kill a man in return for a woman and two men in return for a man. The other tribe refused this. Then they brought the matter before the Prophet (peace and blessings be upon him). The Prophet (peace and blessings be upon him) said: "Killing is a matter of equality." So the people reached a settlement among themselves on blood money. They considered sufficient the blood money of a man for a man, the blood money of a woman for a woman, and the blood money of a slave for a slave. And he (peace and blessings be upon him) ruled for one of the two tribes over the other in this way. The narrator said: That ruling is the saying of Allah, the Lord of Might: "O you who believe, retaliation for the slain has been prescribed for you: a free man is to be killed for a free man, a slave for a slave, and a woman for a woman" [Al-Baqarah: 178].
Sufyan bin Husayn said: The verse: "But whoever is forgiven anything of the retaliation by his brother." He said: What is meant is that whoever has granted his brother some favor in it should pay him in a fair manner, and the claimant should follow it up in an excellent way, up to the saying of Allah, the Lord of Might: "a painful punishment."