Imam al-Nawawi said:
“Neither prohibition nor praiseworthiness has been established for the month of Rajab in itself, HOWEVER,
(1) the principle concerning fasting is that it is praiseworthy in itself, and
(2) in the Sunan of Abu Dawud the Prophet has made the fasting of the sacred months praiseworthy, and Rajab is one of them.”
A Hadith On Fasting in Rajab
- `Uthman ibn Hakim al-Ansari said: “I asked Sa`eed ibn Jubayr about fasting in Rajab, and we were then passing through the month of Rajab, whereupon he said: “I heard Ibn `Abbas saying: “The Messenger of Allah used to observe fast so continuously that we thought he would not break it, and did not observe it so continuously that we thought he would not observe fast.” Muslim and Abu Dawud relate it in Kitab al-sawm, respectively in the chapter on fasting at times other than Ramadan, and in the chapter of fasting during Rajab.