Abu Dawud Book 34, Hadith Number 4503.

Chapter : If a man kills his slave or cuts off one of his limbs retaliation will be taken on him.

Narated By N/A : Qatadah transmitted the tradition mentioned above through a chain of narrators like that of Shu’bah. This version adds: Then al-Hasan forgot this tradition, and he used to say: A free man is not to be killed for a slave.