Musnad Ahmad 1153:1840

Hajjaj narrated to us, he said: Layth narrated to us, he said: Yazid ibn Abi Habib narrated to me, from ‘Arak ibn Malik, from ‘Urwah, that ‘Aishah informed him that the Messenger of Allah (may Allah bless him and grant him peace) used to pray thirteen rak'ahs at night, including the two rak'ahs of the dawn prayer.