Musnad Abu Ya'la al-Mawsili 149:17

Abu Ma'mar Isma'il ibn Ibrahim narrated to us, Abd al-Salam ibn Harb narrated to us, from Budayl ibn Maysarah, from Abu al-Jawza', from 'Aishah, that the Messenger of Allah (may Allah bless him and grant him peace) would not increase in the two rak'ahs beyond the tashahhud.