Musnad Ahmad 1153:1484

Muhammad ibn Yazid narrated to us, from Ayyub—meaning Abu al-Ala’ al-Qassab—from Abu Hashim, from Hisham ibn Urwah, from his father, from Aisha: "The Messenger of Allah (peace and blessings of Allah be upon him) used to pray while sitting. When he wanted to bow, he would stand up, recite the equivalent of ten verses, or whatever Allah willed, and then he would bow."