Musannaf Ibn Abi Shayba 13:1948

Abu Bakr narrated to us, he said: Waki’ narrated to us, from al-Hakam, from Abu al-Fudayl, he said: I heard al-Hasan—and he was asked about a man who bargains with a man for a slave (to be set free), and he says, "I do not have [the money]," so he says, "Buy him, until I buy him from you"—and he disliked it and said: "This is *al-muwasafah* (bargaining/negotiating)."