Mishkat al-Masabih #1944

‘A'isha said, "God’s messenger used to fast to such an extent that we thought he would never break his fast, and he would go without fasting to such an extent that we thought he would never fast. I never saw God’s messenger fast a complete month except in Ramadan, and I never saw him fast more in any month than in Sha'ban." In a version she said he used to fast the whole of Sha'ban, i.e. he would fast all but a little of Sha'ban. (Bukhari and Muslim.)