Yahya related to me from Malik from Abu'n Nadr, the mawla of Umaribn Ubaydullah, from Abu Salama ibn Abd ar-Rahman that A'isha, thewife of the Prophet, may Allah bless him and grant him peace, said,"The Messenger of Allah, may Allah bless him and grant him peace, usedto fast for so long that we thought he would never stop fasting, andhe would go without fasting for so long that we thought he would neverfast again. I never saw the Messenger of Allah, may Allah bless himand grant him peace, fast for a complete month except for Ramadan, andI never saw him do more fasting in any one month than he did inShaban.'
USC-MSA web (English) reference: Book 18, Hadith 56
Arabic reference: Book 18, Hadith 689