Musannaf Ibn Abi Shayba 27:569

Muhammad ibn Bishr narrated to us, he said: Zakariya narrated to us, from ‘Amir, that ‘Ali married Asma’ bint ‘Umays. Her two sons, Muhammad ibn Ja’far and Muhammad ibn Abi Bakr, boasted to one another. Each of them said, "I am more noble than you, and my father is better than your father." ‘Ali said to her, "Judge between them." She said, "I have not seen a youth among the Arabs better than Ja’far, and I have not seen a mature man who was better than Abu Bakr." ‘Ali said to her, "You have left nothing for us. Had you said anything other than this, I would have despised you. By Allah, the three of whom you are the least are indeed the best."