Hadith 3580
Sayyidah Aisha Siddiqa (may Allah be pleased with her) narrates: The Prophet Muhammad (peace and blessings be upon him) never fasted an entire month except for Ramadan, nor did he ever leave fasting for an entire month. The Prophet (peace and blessings be upon him) did not fast in any other month as much as he fasted in Sha'ban.
Hadith 3581
Sayyiduna Abdullah bin Amr (may Allah be pleased with him) narrates this statement of the Prophet Muhammad (peace and blessings be upon him): "Whoever always (i.e., daily) observes voluntary fasting, then in reality, he has neither fasted nor left fasting."