'Imran b. Husain Radiallah Anho reported Allah's Messenger Sallallahu alaihi wasallam having said to him or to someone else: Did you fast in the middle of Sha'ban? He said: No. Thereupon he (the Holy Prophet) said: If you did not observe fast, then you should observe fast for two days.

Sahih Muslim. The Book of Fasting

-----------------------------------------

Narrated 'Aisha Radiallah Anha,  Allah's Apostle Sallallahu alaihi wasallam  used to fast till one would say that he would never stop fasting, and he would abandon fasting till one would say that he would never fast. I never saw Allah's Apostle fasting for a whole month except the month of Ramadan, and did not see him fasting in any month more than in the month of Sha'ban.

Sahih Al Bukari

-----------------------------------------