Musannaf Ibn Abi Shayba 18:728

Abu Bakr narrated to us, he said: Waki’ narrated to us, he said: Sufyan narrated to us, from ‘Abdullah ibn Dhakwan Abu al-Zinad, from ‘Umar ibn ‘Abd al-‘Aziz, who said: The blood money (diyah) of the mu’ahid (a non-Muslim under a covenant of protection) is half of the blood money of the Muslim.