A sister asked this question: “As-salamu alaykum. I would like to ask whether it is recommended to fast frequently during the months of Rajab and Sha`ban or not”
Fasting is a spiritual act of worship, which elevates one to the rank of angels, as one abstains from eating, drinking, and sexual relations from dawn until sunset.
In general, a Muslim should fast some days now and then; in these days, one abstains from worldly matters, strengthens his or her resolution, and purifies his or her soul.
Fasting in Rajab
However, no authentic hadiths are stated indicating that the Prophet (peace be upon him) recommended fasting in Rajab, nor did he forbid fasting in it, according to Imam An-Nawawi, who added that fasting is recommended.
But the permissibility of fasting in Rajab is based on the narration of Abu Dawud who reported that Allah’s Messenger recommended fasting during the Four Sacred Months, among which is the month of Rajab.
Fasting in Shaban
As for the month of Shaban, there are authentic hadiths about the virtue of fasting during it, among which the hadith recorded in Sahih Muslim on the authority of Aishah who said, “Allah’s Messenger used to observe fasting (continuously) that we would say he would not breakfasting, and he used not to fast (continuously) until we would say he would not fast. And I did not see Allah’s Messenger completing the fast of a month, except Ramadan, and I did not see him fasting more in any other month than in Shaban.”
The hadith indicates that the Messenger used to fast many days in Shaban that Lady Aishah may Allah raise her rank said in another narration, “He [the Prophet] used to fast (almost) all of Shaban; he used to fast Shaban except for few (days).”
Except for these two months, Allah’s Messenger used to observe fasting continuously to the extent that people would say that he would not break fasting.
He also used to keep breaking the fast for many consecutive days to the extent that people would say that he would not fast.
So, the matter depends on feeling comfortable and devoted to worship without feeling bored or weary. That is why the Prophet said, “Do (good) deeds that are within your capacity, as Allah never gets tired of giving rewards until you get tired of doing good deeds.” (Al-Bukhari and Muslim)
The Prophet also said, “The most beloved deed to Allah is the one its doer performs regularly even if it were little.” (Muslim)