Zirr bin Hubaysh (may Allah have mercy on him) says: I said to Sayyiduna Ubayy bin Ka'b (may Allah be pleased with him): O Abu al-Mundhir, I want to go for jihad, so I will come to Iraq and give loans. He said: You are in a land of usury, where usury is widespread. When you lend to someone and he gives you a gift, take your loan back and return his gift to him.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب البيوع / 10928