Musannaf Ibn Abi Shayba 13:644

Abu Bakr narrated to us, he said: Ibn Fudayl narrated to us, from his father, from Abu Hazim, from Abu Hurayrah, who said: The Messenger of Allah (may Allah bless him and grant him peace) said: "Wheat for wheat, and barley for barley, hand to hand, measure for measure, and weight for weight. So whoever gives more or asks for more has committed usury (riba), except for what differs in its colors."