Musannaf Ibn Abi Shayba 18:504

Abu Bakr narrated to us, he said: Abd al-A’la narrated to us, from Ma’mar, from al-Zuhri, from Sa’id ibn al-Musayyib, who said: The wound of a slave is like the wound of a free person in its blood money (diyah). Al-Zuhri said: Some people said: It is only property, so it is according to the amount that is diminished from his price.