Musannaf Ibn Abi Shayba 18:707

Abu Bakr narrated to us, he said: Abd al-Rahim narrated to us, from Ash'ath, from al-Hasan and al-Sha'bi, they both said: The mistake (unintentional killing) is upon the *'Aqilah* (the paternal relatives of the killer who pay the blood money). And the intentional (killing) and the settlement are upon the one who committed it, from his own wealth.