Musannaf Ibn Abi Shayba 13:2159

Abu Bakr narrated to us, he said: Abd al-Salam narrated to us, from Ash'ath, from Ibn Sirin, regarding the man who pays a dirham in advance to a grocer: He said: He should not take except that which he paid in advance for. And if he deposits it with him, then let him take whatever he wishes.