Musnad Ahmad 1153:64

'Abd al-Rahman narrated to us, Malik narrated to us, from Sa'id ibn Abi Sa'id, from Abu Salamah, who said: I asked 'Aishah about the prayer of the Messenger of Allah (may Allah bless him and grant him peace) in Ramadan. She said: "The Messenger of Allah (may Allah bless him and grant him peace) would not increase in Ramadan or any other time beyond eleven rak'ahs. He would pray four, and do not ask about their beauty and their length. Then he would pray four, and do not ask about their beauty and their length. Then he would pray three." She said: I said: "O Messenger of Allah, do you sleep before you perform the witr?" He said: "O 'Aishah, my eyes sleep, but my heart does not sleep."