Musnad Ahmad 1153:1065

Waki’ narrated to us, Kahmas narrated to us, from ‘Abdullah ibn Shaqiq, who said: I asked ‘Aishah about the fasting of the Messenger of Allah (peace and blessings of Allah be upon him). She said: "I did not know him to fast a full month, except that he would break his fast during it, nor did he break his fast [for a full month], except that he would fast during it, until he passed away."