Musnad Ahmad 1153:1787

'Abd al-Malik ibn 'Amr narrated to us, Ibn Abi Dhi'b narrated to us, from al-Zuhri, from 'Urwah, from 'Aishah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) used to pray between the time he finished the 'Isha prayer—which is what you call or name al-'Atamah—until the dawn, eleven prostrations. He would say the taslim between every two prostrations, and he would perform witr with one. He would prostrate in his prayer for the duration of what one of you would take to recite fifty verses before he raised his head. When the mu'adhdhin fell silent from the first call for the morning prayer, he would pray two light rak'ahs, then he would lie down on his right side, until the mu'adhdhin came to him, and he would go out with him.