Musannaf Ibn Abi Shayba 13:3446

Abu Bakr narrated to us, he said: Abdullah ibn Numayr narrated to us, from al-Rabi’ ibn Sa’d, who said: I asked Abu Ja’far about a man from whom I buy food, so he gives me some of it, then he is cut off regarding it and does not find what to give me, so he says: "Sell me from your food until I pay him back." He said: "Do not approach this; this is clear usury (riba)."