Sahih Bukhari
Sahih Bukhari Volume 003, Book 031, Hadith Number 190.
Hadith Section/Book: Sahih Bukhari Sahih Bukhari Book 31. Fasting
Narated By 'Aisha : Allah's Apostle used to fast till one would say that he would never stop fasting, and he would abandon fasting till one would say that he would never fast. I never saw Allah's Apostle fasting for a whole month except the month of Ramadan, and did not see him fasting in any month more than in the month of Sha'ban.