Sahih Bukhari Volume 5, Book 57, Hadith Number 89.

Narated By Abu Bakra : I heard the Prophet talking at the pulpit while Al-Hasan was sitting beside him, and he (i.e. the Prophet) was once looking at the people and at another time Al-Hasan, and saying, “This son of mine is a Saiyid (i.e. chief) and perhaps Allah will bring about an agreement between two sects of the Muslims through him.”