The Mother of the Believers, Sayyidah Aishah (may Allah be pleased with her), narrates that the Messenger of Allah (peace and blessings be upon him) used to fast until we would say that he would never break his fast, and when he went without fasting we would say that he would never fast. And I never saw him fast a complete month other than Ramadan, and he used to fast most in Sha'ban.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 8427