Musnad Ahmad 1153:1808

Isma'il narrated to us, from al-Walid ibn Abi Hisham, from Abu Bakr ibn Muhammad ibn 'Amr ibn Hazm, from 'Amrah, from 'Aishah, who said: "The Messenger of Allah (peace and blessings of Allah be upon him) used to recite while he was sitting. Then, when he wanted to bow, he would stand for the duration of what a person would take to recite forty verses."