Musnad Ahmad 30:3528

Aswad ibn Amir narrated to us, Kamil and Abu al-Mundhir narrated to us, Kamil said: Aswad said: The meaning was reported to us from Abu Salih, from Abu Hurairah, who said: We used to pray the Isha prayer with the Messenger of Allah, peace and blessings of Allah be upon him. When he prostrated, al-Hasan and al-Husayn would jump onto his back. When he raised his head, he would take them with his hand from behind him, a gentle taking, and place them on the ground. When he returned [to prostration], they would return, until he finished his prayer, then he sat them on his thighs. He said: So I stood up to him and said: "O Messenger of Allah, shall I take them back [to their mother]?" Then a flash of lightning occurred, and he said to them: "Go to your mother." He said: So its light remained until they entered.