Sahih al-Bukhari 62:91
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
Sahih al-Bukhari 62:91
In-book reference
Book 62, Hadith 91
Arabic Text
حَدَّثَنَا صَدَقَةُ، حَدَّثَنَا ابْنُ عُيَيْنَةَ، حَدَّثَنَا أَبُو مُوسَى، عَنِ الْحَسَنِ، سَمِعَ أَبَا بَكْرَةَ، سَمِعْتُ النَّبِيَّ صلى الله عليه وسلم عَلَى الْمِنْبَرِ وَالْحَسَنُ إِلَى جَنْبِهِ، يَنْظُرُ إِلَى النَّاسِ مَرَّةً وَإِلَيْهِ مَرَّةً، وَيَقُولُ " ابْنِي هَذَا سَيِّدٌ، وَلَعَلَّ اللَّهَ أَنْ يُصْلِحَ بِهِ بَيْنَ فِئَتَيْنِ مِنَ الْمُسْلِمِينَ ".