It is narrated from Sayyiduna Abu Umamah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "A borrowed item must be returned." A man said: "O Messenger of Allah, what do you say about the covenant of Allah?" He said: "The covenant of Allah has the greatest right to be fulfilled."
Hadith Referenceالمعجم الكبير للطبراني / باب الصاد / 7617