I have heard that one must fast on the following days of Rajab,
1st day of Rajab; 1st Friday night (Thursday night in Islam) Night of Wishes; on the 15th day of Rajab; on the 27th Mi’raaj Night; and on the 30th day of Rajab.
Is this sunnah or bid‘ah?
There is no saheeh report from the Prophet (Sallallaahu ‘Alayhi wa Sallam) or from the Sahaabah to indicate that there is any particular virtue in fasting during Rajab.
The fasting that is prescribed in Rajab is the same as that prescribed in other months, namely fasting on Mondays and Thursdays, and the three days of al-Beed, fasting alternate days, and fasting Sirar al-Shahr. Some of the scholars said that Sirar al-Shahr refers to the beginning of the month; others said that it refers to the middle or end of the month. ‘Umar (RadiyAllaahu ‘anhu) disliked fasting in Rajab because it involved resemblance to the Jaahiliyyah. It was reported that Kharashah ibn al-Harr said: I saw ‘Umar smacking the hands of those who fasted in Rajab until they reached out for food, and he was saying, This is a month which was venerated in the Jaahiliyyah. (al-Irwaa’, 957; al-Albaani said: it is saheeh).
Ibn al-Qayyim (rahimahullah) said: the Prophet (Sallallaahu ‘Alayhi wa Sallam) did not fast for three consecutive months (i.e., Rajab, Sha’baan and Ramadaan) as some people do, and he never fasted Rajab at all, nor did he encourage people to fast this month.
Al-Haafiz ibn Hajar (rahimahullah) said in Tabayyun al-‘Ajab bimaa wurida fi Fadl Rajab:
No saheeh hadeeth that may be used as evidence has been narrated concerning the virtues of the month of Rajab or fasting this month or fasting in any specific part of it, or observing Qiyaam al-Layl specifically during this month.
In Fataawa al-Lajnah al-Daa’imah it states: with regard to fasting specifically in Rajab, we do not know of any basis in Sharee’ah for doing that.
Shaykh Muhammad Saalih al Munajjid