From Sahih Bukhari (Hadith 6716):
Narrated `Amr:Jabir said: An Ansari man made his slave a Mudabbar and he had no other property than him. When the Prophet (ﷺ) 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
Reference: Bukhari 6716