Musnad Ahmad 459:9

'Abd al-Rahman ibn Mahdi narrated to us, he said: Mu'awiyah ibn Salih narrated to us, from Sa'id ibn Hani', he said: I heard al-'Irbad ibn Sariyah say: I sold a young camel to the Prophet, may Allah bless him and grant him peace, and I came to him to demand payment for it. I said: "O Messenger of Allah, pay me the price of my young camel." He said: "Delay, I will not pay you for it except with a young camel." He said: So he paid me, and he made my payment excellent. He said: A Bedouin came to him and said: "O Messenger of Allah, pay me for my young camel." So the Messenger of Allah, may Allah bless him and grant him peace, gave him on that day a camel that had reached a mature age. He said: "O Messenger of Allah, this is better than my young camel." He said: The Messenger of Allah, may Allah bless him and grant him peace, said: "Indeed, the best of the people is the best of them in repayment."