Sahih Muslim Book 15, Hadith Number 4115.

Chapter : The permissibility of buying a mudabbar slave.

Jabir b. ‘Abdullah said that a person among the Ansar declared his slave free after his death, as he had no other property. This news reached the Apostle of Allah (may peace be upon him) and he said: Who will buy him from me? And Nu’aim b. al-Nahham bought him for eight hundred dirhams and he handed them over to him, ‘Amr (one of the narrators) said: I heard Jabir b. ‘Abdullah as saying: He was a Coptic slave, and he died in the first year (of the Caliphate of ‘Abdullah b. Zubair).