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
Abu Salamah says: I asked Sayyidah Aishah (may Allah be pleased with her) about the fasting of the Messenger of Allah (peace and blessings be upon him). She said: He used to fast until we would say: he will only keep fasting. And when he went without fasting, we would say that he will only keep not fasting. And I never saw him fast more in any month than in Sha'ban. He would fast the whole of Sha'ban except for a few days.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 8428
Sayyidah Aishah (may Allah be pleased with her) narrates that in the time of the Messenger of Allah (peace and blessings be upon him), if one of us missed fasts, she would not be able to make them up because of him until Sha'ban came. The most fasting that he did was in Sha'ban; indeed, he would fast the whole month except for a few days.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 8429
Sayyidah Aishah (may Allah be pleased with her) narrates that the most beloved of all the months to him (peace and blessings be upon him) in which to fast was Sha'ban; then he would join Ramadan to it.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 8430