Musannaf Ibn Abi Shayba 13:770

Abu Bakr narrated to us, he said: Waki’ narrated to us, from Sufyan, from ‘Abdullah ibn Abi al-Safar, from al-Sha’bi: That he disliked for one to say, "I buy from you what is owed by so-and-so." And he said: "It is *gharar* (uncertainty/risk)."