It is narrated from Sayyiduna Abu Shurayh al-Ka'bi (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "O people of Khuza'ah! This man of Hudhayl whom you have killed, I am paying his blood money. If anyone kills after this statement of mine, the victim's family will have the choice between two matters: either they take the blood money or they kill."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنايات / 16063