No specific Hadiths were authentically reported about the merit of Sawm in Rajab, except that which was
Abu Dawud, and ranked as Sahih (authentic) by
on the authority of
Usamah who said:
I asked, ‘O Messenger of Allah, I have not seen you fast in a month as much as you fast in Sha‘ban.’ He (peace be upon him) said, ‘This is a month between Rajab and Ramadan that people overlook. It is a month in which deeds are raised to the Lord of the worlds, and I love that my deeds be raised while I am fasting.’
General Hadiths were mentioned about encouraging Sawm for three days of every month;
Sawm on the White Days, (Part No. 2; Page No. 509) which are the 13th, 14th, and 15th of every Hijri (lunar) month;
Sawm in the Sacred, Inviolable Months; and Sawm every Monday and Thursday. The same applies to the month of Rajab. If you are keen on choosing some days to fast on, you can fast on the White Days or Mondays and Thursdays. Otherwise, the matter is open to choice. As for dedicating certain days in Rajab to Sawm, we do not know of any basis for it in Shari‘ah (Islamic law).May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.