Musnad Ahmad 30:1985

Al-Fadl ibn Dukayn narrated to us, he said: Sufyan informed us, from Salamah ibn Kuhayl, from Abu Salamah, from Abu Hurayrah, who said: A man had a claim against the Prophet, peace and blessings of Allah be upon him, for a camel of a certain age. He came to him demanding payment, so they searched for one for him, but they found nothing except a camel of an age older than his. He said: "Give it to him." The man said: "You have fulfilled my right, may Allah fulfill yours." The Messenger of Allah, peace and blessings of Allah be upon him, said: "Indeed, the best of you are those who are the best in fulfilling their obligations."