Alqamah bin Wa'il (may Allah have mercy on him) said that his father (Wa'il bin Hujr, may Allah be pleased with him) told him that he was sitting with the Prophet (peace and blessings be upon him) when a man came seeking retaliation from another, and he said: O Messenger of Allah, this man killed my brother. The Messenger of Allah (peace and blessings be upon him) said: "Did you kill him?" He said: If he does not confess, I will establish witnesses against him. He (the accused) said: Yes. He (peace and blessings be upon him) asked: "How did you kill him?" He replied: We were both beating leaves down from a tree when he insulted me; I became angry, struck him on the head with an axe, and he died. So he (peace and blessings be upon him) said: "Do you have anything to pay as blood money?" He said: This cloak of mine. He said: "What do you think, will your people buy you (pay the ransom for you)?" He said: I am even more worthless than that to my people. He (peace and blessings be upon him) placed the man's strap in that man's hand and said: "Take him and take your retaliation." He took hold of him and went off, and he (peace and blessings be upon him) said: "If he kills him, he will be like him." A man from the people met him and conveyed to him the words of the Prophet (peace and blessings be upon him). That man came back to the Prophet (peace and blessings be upon him) and said: O Messenger of Allah, I took him by your command, and now I have learned this saying of yours. He said: "Yes; do you not want him to bear your sin and the sin of your brother?" He said: Of course, O Prophet of Allah! He said: "Then that is how it will be." So the man let him go.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنايات / 16051