Musannaf Ibn Abi Shayba 18:710

Abu Bakr narrated to us, he said: Hammad bin Khalid narrated to us, from Malik bin Anas, from al-Zuhri: He said: The Sunnah has passed that the *'aqilah* (the paternal relatives) do not pay the blood money for intentional homicide, except by their own free will.