Musannaf Ibn Abi Shayba 3:6379

Abu Bakr narrated to us, he said: Waki’ narrated to us, he said: Hisham ibn ‘Urwah narrated to us, from his father, from ‘Aishah, she said: The Messenger of Allah (may Allah bless him and grant him peace) used to pray at night, and I would be lying down between him and the Qiblah. When he intended to perform the Witr, he would wake me up, and I would perform the Witr.