Musannaf Ibn Abi Shaybah

Hazrat Muhammad bin Abu Ja'd says that I asked Hazrat Sha'bi (may Allah have mercy on him) about buying the clay of a goldsmith. He disliked its sale and said, "This is deception." Hazrat Muhammad (may Allah have mercy on him) says, "My father used to sell it in exchange for something present (i.e., hand to hand sale)."