Musnad Abu Ya'la al-Mawsili 150:291

Hannad ibn al-Sari narrated to us, 'Abdah ibn Sulayman narrated to us, from al-Mas'udi, from Yunus ibn 'Ubayd, from 'Abdullah ibn Mu'qil, from 'A'ishah, who said: When the Messenger of Allah (may Allah bless him and grant him peace) prayed standing, he would bow standing, and when he prayed sitting, he would bow sitting.