From Sahih Bukhari (Hadith 3746):
Narrated Abu Bakra:I heard the Prophet (ﷺ) 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
Reference: Bukhari 3746