Sahih Muslim Book 6, Hadith Number 2577.

Chapter : The fasts observed by the Apostle of Allah (may peace be upon him) besides Ramadhan.

‘Abdullah b. Shaqiq reported: I said to ‘Aisha (Allah be pleased with her): Did the Messenger of Allah (may peace be upon him) observe fast during a month? She said, I do not know of any month in which he fasted throughout except Ramadan and (the month) in which he did not fast at all till he ran the course of his life. May peace be upon him.