Musannaf Ibn Abi Shayba 18:1275

Abu Bakr narrated to us, he said: Ghundar narrated to us, from Shu'bah, he said: I asked al-Hakam and Hammad about a free man and a slave who collided and both died. They said: As for the blood money (diyah) of the free man, it is not upon the slave. And as for the blood money of the slave, it is upon the 'aqilah (the paternal relatives).