Question:
What are the days that should be fasted (for being a confirmed act of Sunnah)? What is the ruling on fasting the first day of the Hijri year, the fifteenth of Rajab and so on?
Fatwa:
All perfect praise be to Allah, the Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His Slave and Messenger.
The only obligatory days of fasting are the days of the month of Ramadan. Fasting may also be obligatory because of other reasons such as compensating certain days that one did not fast in Ramadan, vowed fasting and fasting of expiations. As for voluntary fasting, it is preferable (i.e., recommended) such as fasting the Day of ‘Arafah, the tenth and the ninth of Muharram, the Monday and Thursday of every week and the three days of the full moon (the 13th-14th-15th of every month), fasting one day and breaking the fast the following day and fasting six days in the month of Shawwaal. Nevertheless, some of these days are more confirmed than others, that is, some of these days are more favorable and entail more reward. The most confirmed day among these days is fasting the Day of ‘Arafah (for non-pilgrims) then the tenth of Muharram and then the six days of Shawwaal.
There are many Hadeeths that indicate the virtue of fasting these days. It was narrated on the authority of Abu Qataadah, may Allah be pleased with him, that the Prophet said: "Fasting the Day of ‘Arafah atones for the sins of two years: the preceding and the coming years, and fasting the Day of ‘Aashooraa’ (Tenth of Muharram) atones for the sins of the preceding year." [Saheeh: Ahmad] The Prophet also said: "Whoever fasts Ramadan and then follows it with fasting six days of Shawwaal, it would be as if he fasts perpetually." [Muslim, Abu Daawood, Ibn Maajah, Ahmad and At-Tirmithi]
Fasting the first day of the Hijri year is a Bid‘ah (religious innovation) as there is no text that supports it. This ruling applies unless this day coincides with a certain day that one usually fasts (i.e., coincinding with a Monday or a Thursday one who is used to fasting these two days weekly). This also applies if the days that one fasts coincide with some days of the month of Rajab without specifying a certain day of it such as the fifteenth as the Hadeeths that indicated this are weak. Ibn Hajar said, “No sound Hadeeth that could be cited as proof was narrated regarding the virtue of the month of Rajab, fasting during it or praying at night on a certain day specifically.”
Allah Knows best.