Muwatta Imam Malik (Riwayat Ibn al-Qasim)

And with this chain of narration, (it is narrated from Sayyidah Aisha, may Allah be pleased with her) that the Messenger of Allah, peace and blessings be upon him, would begin to fast continuously until we would say that he will not break his fast, and he would begin to break his fast until we would say that he will not fast. I did not see the Messenger of Allah, peace and blessings be upon him, fast an entire month except for Ramadan, and I did not see him fast more in any month than in Sha'ban.