Musannaf Ibn Abi Shayba 18:1077

Abu Bakr narrated to us, he said: Abd al-Rahman ibn Mahdi narrated to us, from Sufyan, from Ibn Abi Dhi'b, from a man, from Sa'id ibn al-Musayyib, he said: The *'aqilah* (the paternal relatives responsible for blood money) shall not pay blood money except for one-third, and whatever is in excess of that.