Sahih Bukhari Volume 4, Book 56, Hadith Number 742.

Narated By ‘Uqba bin Al-Harith : (Once) Abu Bakr offered the ‘Asr prayer and then went out walking and saw Al-Hasan playing with the boys. He lifted him on to his shoulders and said, ” Let my parents be sacrificed for your sake! (You) resemble the Prophet and not ‘Ali,” while ‘Ali was smiling.