Sa'id bin Abi Burdah narrates from his father Abu Burdah (may Allah have mercy on him): I came to Madinah and met Sayyiduna Abdullah bin Salam (may Allah be pleased with him), and he said: Will you not come home so that I may feed you sawiq and dates? We went, and he fed us sawiq and dates, then he said: You are in a land where usury (riba) is widespread. When a man owes you a debt and he gives you as a gift a bundle of dry fodder tied with rope, or of barley, or of straw, do not accept it, for that is usury.
(b) Sayyiduna Ubayy bin Ka'b (may Allah be pleased with him) narrated a similar story about a loan and a gift.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب البيوع / 10927