Musannaf Ibn Abi Shayba 13:2561

Abu Bakr narrated to us, he said: Waki’ narrated to us, from Sufyan, from the one who heard Jabir ibn Abdullah saying: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Whoever sells a slave who possesses wealth, then his wealth belongs to the seller, unless the buyer stipulates [otherwise]."