Musnad Ahmad 1153:1177

'Abd al-Razzaq narrated to us, Malik informed us, Salim Abu al-Nadr, the freed slave of 'Umar ibn 'Ubayd Allah, narrated to us, from Abu Salamah ibn 'Abd al-Rahman, that 'Aishah said: "The Messenger of Allah (may Allah bless him and grant him peace) would fast until we would say: 'He does not break his fast,' and he would break his fast until we would say: 'He does not fast.' And I never saw the Messenger of Allah (may Allah bless him and grant him peace) complete the fasting of an entire month except for Ramadan, and I never saw him in any month fast more than he did in Sha'ban."