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: now he will not break his fast; and he would go without fasting until we would say: now he will not fast. I never saw him fast a complete month except Ramadan, and I never saw him fast more in any month than in Sha'ban.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 8471
Alqamah says: I said to Aishah (may Allah be pleased with her): "Did the Messenger of Allah (peace and blessings be upon him) use to single out any days (for fasting)?" She said: "No. His practice was constant, and which of you is able to do what he was able to do?"
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 8472