Musannaf Ibn Abi Shayba 3:1546

'Abdah narrated to us, from Hisham, from his father, from 'Aishah, who said: The Messenger of Allah (may Allah bless him and grant him peace) used to pray the night prayer standing. When he advanced in age, he began to pray sitting. When thirty or forty [verses] remained for him, he would stand, recite them, and then prostrate.