Musannaf Ibn Abi Shayba 18:858

Abu Bakr narrated to us, he said: Kathir ibn Hisham narrated to us, from Ja'far ibn Burqan, that Umar ibn Abd al-Aziz wrote: If he did not leave any relatives except for his freed slaves, they would be the most entitled of people to his inheritance. Therefore, impose upon them his blood money (diya), just as they inherit from him.