Musnad Ahmad 1153:564

Abu al-Yaman narrated to us, he said: Shu'ayb informed us, from al-Zuhri, he said: 'Urwah ibn al-Zubayr informed me that 'Aishah informed him: "The Prophet, peace and blessings of Allah be upon him, used to pray eleven rak'ahs at night. That was his prayer. He would perform the prostration during that for the duration of what one of you would take to recite fifty verses before he would raise his head. And he would pray two rak'ahs before the dawn prayer, then he would lie down on his right side until the caller came to him for the prayer."