Musnad Abu Ya'la al-Mawsili 108:217

Ubayd Allah ibn Umar narrated to us, Hammad narrated to us, from Amr, from Jabir: That a man from the Ansar emancipated a slave of his, and he had no wealth other than him. He said: This reached the Messenger of Allah, may Allah bless him and grant him peace, so he said: "Who will buy him from me?" So Nu'aym ibn Abdullah bought him for eight hundred [dirhams], and he handed them over to him. He said: I heard Jabir saying: "A Coptic slave who died last year."