Musannaf Ibn Abi Shayba 18:502

Abu Bakr narrated to us, he said: Hafs narrated to us, from Ash'ath, from al-Hakam and Hammad, from Ibrahim, who said: The wound of a slave is [calculated] from his price, just as the wound of a free person is [calculated] from his blood money: a tenth and half of a tenth.