Musnad Abu Ya'la al-Mawsili 150:381

Narrated to us Mujahid ibn Musa, narrated to us Isma'il ibn Ibrahim, from al-Walid ibn Abi Hisham, from Abu Bakr ibn Muhammad ibn 'Amr ibn Hazm, from 'Urwah, from 'Aishah, who said: The Messenger of Allah (may Allah bless him and grant him peace) used to recite while he was sitting. When he intended to bow, he would stand for the duration of what a person would take to recite forty verses.