Musnad Ahmad 1153:805

Abu Ahmad Muhammad ibn Abdullah al-Zubayri, the freed slave of Banu Asad, narrated to us, saying: Sufyan narrated to us, from Ayyub, from Muhammad, from Abdullah ibn Shaqiq, from Aisha, who said: The Messenger of Allah (peace and blessings of Allah be upon him) would pray a long night standing, and a long night sitting. I said: "How did he do it?" She said: "When he recited while standing, he would bow while standing, and when he recited while sitting, he would bow while sitting."