Musnad Ahmad 1153:1984

Yazid narrated to us, he said: Muhammad—meaning Ibn ‘Amr—informed us, from Muhammad ibn Ibrahim, that he heard ‘Alqamah ibn Waqqas al-Laythi say: I asked ‘A’ishah, I said: "How did the Messenger of Allah, peace and blessings of Allah be upon him, pray the two rak'ahs while he was sitting?" She said: "He would recite in them while he was sitting, and when he wanted to bow, he would stand up and then bow."