Yazid bin Abi Yahya says: I asked Sayyiduna Anas bin Malik (may Allah be pleased with him): O Abu Hamzah, a man among us lends money to his brother, and then he gives him a gift. He said that the Messenger of Allah (peace and blessings be upon him) said: "When one of you gives a loan, and then he is given a gift in return or is given a ride, he should not accept it, unless there was already some (such) relationship between them before that."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب البيوع / 10934