With regard to fasting the month of Rajab, there is no saheeh hadeeth to indicate that there is any special virtue in fasting all or part ofthis month.
What some people do, singling out some days of Rajab for fasting, believing that they are better than others, has no basis in sharee’ah.
But there is a report from the Prophet (peace and blessingsof Allaah be upon him) which indicates that it is mustahabbto fast during the sacred months (and Rajab is one of the sacred months). The Prophet (peace and blessingsof Allaah be upon him) said: “Fast some days of the sacred months and not others.” Narrated by Abu Dawood, 2428; classed as da’eef by al-Albaani in Da’eefAbi Dawood.
Even if this hadeeth were saheeh, it indicates that it is mustahabb to fast during the sacred months. So if a person fasts during Rajab because of this, and he also fasts in the other sacred months, there is nothing wrong with that. But singling out Rajab for fasting is not right.
Shaykh al-Islam Ibn Taymiyah(may Allaah have mercy on him) said in Majmoo’ al-Fataawa (25/290):
As for fasting in Rajab in particular, the ahaadeeth concerning that are all da’eef(weak), and in fact mawdoo’ (fabricated). The scholars do not rely on any of them. Theyare not among the da’eef ahaadeeth which have been narrated concerning virtues, rather most of them are fabricated and false. In al-Musnad and elsewhere there is a hadeeth which says that the Prophet (peaceand blessings of Allaah be upon him) enjoined fasting the sacred months, namely Rajab, Dhu’l-Qa’dah, Dhu’l-Hijjah and Muharram, but thishas to do with fasting during all of them, not just Rajab. End quote.
Ibn al-Qayyim (may Allaah have mercy on him) said:
Every hadeeth which mentions fasting in Rajab andpraying during some of its nights is false and fabricated.” End quote from al-Manaar al-Muneef, p. 96
Al-Haafiz ibn Hajar said in Tabyeen al-‘Ajab (p. 11)
There is no saheeh hadeeth that would count as evidencewhich speaks of the virtue ofthe month of Rajab, or that speaks of fasting this month or part of it, or of spending any particular night of it in prayer.
Shaykh Sayyid Saabiq (may Allaah have mercy on him) said in Fiqh al-Sunnah (1/282):
Fasting in Rajab is no better than fasting in any other month, except that it is one of the sacred months. There is no report in the saheeh Sunnah to suggest that thereis anything special about fasting in this month. Whatever has been narratedconcerning that is not fit to be quoted as evidence. End quote.
Shaykh Ibn ‘Uthaymeen (may Allaah have mercy on him) was asked about fasting on the twenty-seventh of Rajab and spending that night in prayer. He replied:
Fasting on the twenty-seventh of Rajab and spending that night in prayeris a bid’ah (innovation), and every bid’ah is a going astray. End quote. Majmoo’ Fataawa Ibn ‘Uthaymeen, 20/440[color=#000099][/color]