Musannaf Ibn Abi Shayba 3:6109

Abu Bakr narrated to us, he said: Ibn ‘Uyaynah narrated to us, from Abu Labid, from Abu Salamah, from ‘Aishah: I said: "Inform me about the prayer of the Messenger of Allah, may Allah bless him and grant him peace." She said: "His prayer at night, in Ramadan and other than it, was thirteen rak'ahs, including the two rak'ahs of Fajr."