Sayyiduna Abu Hurayrah (may Allah be pleased with him) said: The Messenger of Allah (peace and blessings be upon him) stopped at the house of Sayyidah Fatimah (may Allah be pleased with her) and gave the greeting of peace. Hasan or Husayn (one of them, may Allah be pleased with them both) came out, and the Messenger of Allah (peace and blessings be upon him) said to him: "Climb up, may your father be ransomed for you, you are the eye of a gnat," and he took hold of his fingers, and he climbed onto his shoulder. Then the other, Hasan or Husayn, came out, one of his eyes (somewhat) raised, and the Messenger of Allah (peace and blessings be upon him) said to him: "Welcome! Climb up, may your father be ransomed for you, you are the eye of a gnat," and he took hold of his fingers, and he settled on his other shoulder. The Messenger of Allah (peace and blessings be upon him) took hold of the backs of their necks and placed their mouths on his mouth, then said: "O Allah, I love them both, so love them, and love whoever loves them."
Hadith Referenceالمعجم الكبير للطبراني / باب الحاء / 2639