What is the place of the three holy months in Islam and what is the ruling on fasting in these months?
The months of Rajab, Shaban and Ramadan, which are known as three months among the public, are blessed and holy months. When the month of Rajab started, Prophet Muhammad (saw) prayed as, “O Allah! Make the months of Rajab and Shaban blessed for us, and let us reach the month of Ramadan.” (Ibn Hanbal, Musnad, I, 259). It is obligatory to fast in the month of Ramadan (Baqarah, 2/184-185). It is reported in hadith sources that Prophet Muhammad (saw) would perform nafl fasting in Rajab and Shaban relatively more than the other months, but Ramadan was the only month in which he fasted for the whole month (Bukhari, Sawm, 52-53; Muslim, Siyam, 173-79). In this regard, there is no religious basis for fasting in Rajab and Shaban uninterruptedly. One may perform nafl fasting in these months as much as s/he wishes if s/he is healthy and able to perform it.
Source: Presidency Of Religious Affairs The Turkey, High Board of Religious Affairs FATWAS