Musannaf Ibn Abi Shayba 27:540

Hussain bin Ali narrated to us, from Abu Musa, from al-Hasan, who said: The Prophet, may Allah bless him and grant him peace, raised al-Hasan bin Ali with him upon the pulpit and said: "Indeed, this son of mine is a leader (sayyid), and perhaps Allah will reconcile through him between two groups of the Muslims."