From Sahih Muslim (Hadith 4339):
Jabir is reported to have said:A person amongst the Ansar who had no other property declared a slave free after his death. Allah's Messenger (ﷺ) sold him, and Ibn al-Nahham bought him and he was a Coptic slave (who) died in the first year of the Caliphate of Ibn Zubair
Reference: Muslim 4339