Sayyiduna Abu Bakrah (may Allah be pleased with him) says: I saw the Prophet (peace and blessings be upon him) on the pulpit, and Sayyiduna al-Hasan bin Ali (may Allah be pleased with them both) was with him (peace and blessings be upon him). He (peace and blessings be upon him) would look at him once and at the people once, and he said: "This son of mine is a leader. Perhaps Allah will bring about reconciliation between two groups of Muslims through him."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الوقف / 11925