The Book of Fasting (Kitab Al-Sawm)
Muslim :: Book 6 : Hadith 2580
'A'isha, the Mother of the Believers (Allah be pleased with her), reported that the Messenger of Allah (may peace be upon him) used to observe fasts (so conti- nuously) that we said that he would not break, and did not observe (them) till we said that he would not fast: and I did not see the Messenger of Allah (may peace be upon him) completing the fast of a month, but that of Ramadan, and I did not see him fasting more in any other month than that of Sha'ban.