Musnad Ahmad 1:39

Muhammad ibn Abdullah ibn al-Zubayr narrated to us, Umar ibn Sa’id narrated to us, from Ibn Abi Mulaykah, Uqbah ibn al-Harith informed me, he said: I went out with Abu Bakr, may Allah be pleased with him, from the Asr prayer a few nights after the death of the Prophet, may Allah bless him and grant him peace, and Ali, peace be upon him, was walking by his side. He passed by Hasan ibn Ali playing with some boys, so he carried him upon his neck while he was saying: "By my father, he resembles the Prophet, and he does not resemble Ali." He said: And Ali was laughing.