Sahih Bukhari Volume 8, Book 79, Hadith Number 707.

Narated By ‘Amr: Jabir said: An Ansari man made his slave a Mudabbar and he had no other property than him. When the Prophet heard of that, he said (to his companions), “Who wants to buy him (i.e., the slave) for me?” Nu’aim bin An-Nahham bought him for eight hundred Dirhams. I heard Jabir saying, “That was a Coptic slave who died in the same year.”