Musannaf Ibn Abi Shayba 18:508

Abu Bakr narrated to us, he said: Yahya ibn Adam narrated to us, from Hammad ibn Salamah, from Hajjaj, from Husayn al-Harithi, from al-Sha'bi, from al-Harith, from Ali, he said: The wounds of the slaves are treated according to what the wounds of the free are treated upon.