Musnad Ahmad 1153:1205

Abu al-Nadr narrated to us, Muhammad—meaning Ibn Rashid—narrated to us, from Yazid ibn Ya'far, from al-Hasan, from Sa'd ibn Hisham, from Aisha: "That the Messenger of Allah, may Allah bless him and grant him peace, when he prayed the Isha prayer, he would enter the house, then he would pray two rak'ahs, then he would pray after them two rak'ahs longer than them. Then he would perform Witr with three [rak'ahs] in which he would not separate [with a taslim]. Then he would pray two rak'ahs while he was sitting, bowing while he was sitting, and prostrating while he was sitting."