It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that, regarding the saying of Allah Almighty: "And whatever you give in usury (riba) so that it may increase in the wealth of people, it does not increase with Allah" [Surah al-Rum: 39], he said: This is lawful usury: that one gives a gift with the intention of being given more in return. There is no reward in it and no burden (of sin), but the Prophet (peace and blessings be upon him) in particular was forbidden it: "And do not confer a favour to obtain more." [Surah al-Muddaththir: 6]
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 13333