Musnad Ahmad 1153:1429

I read to Abd al-Rahman: Malik, from Hisham ibn Urwah, from his father, from Aisha, that she said: "The Messenger of Allah, peace and blessings of Allah be upon him, used to pray thirteen rak'ahs at night. Then, when he heard the call for the morning prayer, he would pray two light rak'ahs."