Musnad Ahmad 1153:1472

Yazid narrated to us, he said: Muhammad informed us, from Abu Salamah, from Aisha, she said: I said: "O Mother, how was the prayer of the Messenger of Allah, peace and blessings of Allah be upon him, after the last Isha?" She said: "He used to pray thirteen rak'ahs: nine standing, and two sitting, and two after the two calls," meaning between the Adhan of Fajr and the Iqamah.