Sayyiduna Abu Hurayrah (may Allah be pleased with him) narrates: We were praying the Isha prayer with the Messenger of Allah (peace and blessings be upon him), and whenever he (peace and blessings be upon him) prostrated, Sayyiduna Hasan and Sayyiduna Husayn (may Allah be pleased with them both) would climb onto his back. When he intended to bow, he would take hold of them gently with his hand and place them on the ground, and when he returned (to prostration) they would return as well, until he completed his prayer and, having finished, seated them on his thighs. Sayyiduna Abu Hurayrah (may Allah be pleased with him) said: I stood up and went to him and said: O Messenger of Allah, shall I take them? He (peace and blessings be upon him) said: "No." Just then lightning flashed, and he (peace and blessings be upon him) said: "Go to your mother." So they kept walking in its light until they went inside.
Hadith Referenceالمعجم الكبير للطبراني / باب الحاء / 2646