Abu Hurayra reported that the Messenger of Allah, may Allah blesshim and grant him peace, took al-Hasan or al-Husayn by the hand and thenput his feet on top of his own feet and said, "Climb up." (ID)
English reference (ID): Book 14, Hadith 270 (ID)
Arabic reference (ID): Book 1, Hadith 270 (ID)