Musannaf Ibn Abi Shayba 28:939

Jarir narrated to us, from Mughira, from Yazid, from Hammad, from Ibrahim, who said: If a slave fights on a horse belonging to his master, and the spoils are divided for the Muslims, a share is divided for the master’s horse just as it is divided for the horses of the Muslims, and it belongs to his master. And a share is divided for the slave just as it is divided for a man from the Muslims.