It was narrated that Jabir bin 'Abdullah said:
"A man among us promised freedom to a slave after his death, and he did not have any property other than him (this slave). So the Prophet (ﷺ) sold him, and Ibn (Nahham), a man from Banu 'Adi, bought him."
English reference: Vol. 3, Book 19, Hadith 2513
Arabic reference: Book 19, Hadith 2609