Musannaf Ibn Abi Shayba 18:527

Abu Bakr narrated to us, he said: Abu Usamah narrated to us, from Hisham, from al-Hasan, that he said regarding a man whom three people killed. He said: I said, "Do you see that his guardian may pardon some and kill some, and take blood money from some?" He said: "He does not have that right."