Musannaf Ibn Abi Shayba 18:1048

Abu Bakr narrated to us, he said: Yazid narrated to us, he said: Hisham narrated to us, from al-Hasan, regarding a group of people who kill intentionally, and among them is a young boy and a mentally deficient person. He said: It is the blood money of an error [to be paid] by the *‘Aqilah* (the male paternal relatives).