All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
There is disagreement among scholars concerning fasting the month of Rajab. Some scholars believe it is desirable to fast the month of Rajab for the following:
A) General arousal of an interest in fast. This, in fact, is a comprehensive rule with so many proofs.
B) Special arousal of an interest in fasting the sacred months, i.e. Rajab, Thul Qi'dah, Thul Hijjah and Muharram. In addition to that, the majority of Muslim scholars believe that is recommendable to fast those months, especially Rajab. They based their opinion on the following Ahadeeth.
1) Mujeebah al-Baahili reported from his father (or uncle), may Allah be pleased with him, that the Prophet told him: "Fast during the sacred months and leave (fasting), fast during the sacred months and leave" [Ahmad and Abu Dawood and the words of this Hadeeth are of Abu Dawood's narration.]
2) From Usaamah Ibn Zaid, may Allah be pleased with him, who said: "O Allah's Messenger! I never find you fasting in any month like you do during the month of Sha'baan'. The Prophet said: "That is a month the people neglect. It comes between Rajab and Ramadan. It is a month in which the deeds are raised to the Lord of the Worlds. I love that my deeds be raised while I am fasting" [Ahmad and al-Nasaa'i].
ash-Shawkaani said: 'As for the apparent meaning of words; Sha'baan is a month the people (the Prophet’s companions) neglect. It is between Rajab and Ramadan; they mean that it is desirable to fast Rajab since it appears that the Prophet’s companions honor Sha'baan with fasting as they honor Ramadan and Rajab (with fasting). It is also possible that those words mean that the Prophet’s companions, may Allah be pleased with them, honor Sha'baan with fasting as they honor Rajab with sacrifices, since it was a habit of people before Islam to honor it with sacrifices as proven in the Sunnah. But, we think the first opinion is more correct. And Islam effaced the habits and traces of the pre-Islamic period. But, the goal is to state the legality of fasting Rajab from the general and special points of view. In general, there are many Ahadeeth that urge Muslims to fast during the sacred months, and Rajab is one of them. And there are many Ahadeeth concerning legality of unfixed fasts.'
Then, ash-Shawkaani mentioned some Ahadeeth concerning excellence of fasting Rajab as recorded by al-Tabaraani, al-Baihaqi, Abu Nu'aim and Ibn 'Asaakir .
He added: 'as-Subki related from Muhammad Ibn Mansoor al-Sam'aani who said that 'There is no strong narration in the Sunnah concerning desirability of fasting Rajab. Then, all narrations that were related in this matter were weak. According to a narration of Ibn Abi Shaibah that Umar, may Allah be pleased with him, used to beat the hands of people to put them in bowls and say: 'Eat! It is a month that was honored before Islam.' Another narration by Ibn Abi Shaibah from Zaid Ibn Aslam who said: 'Allah's Messenger was asked about the fasting of Rajab and he said: "Why don't you fast in Sha'baan?" Another narration from Ibn 'Umar, may Allah be pleased with him, indicates that it is disliked to fast Rajab.
ash-Shawkaani added: 'It is clear that if special narrations do not constitute a proof to the desirability of fasting during Rajab, general narrations constitute such an evidence, since there is no proof that makes fasting disliked. As for Abu Dawood's narration from Ibn 'Abbaas, may Allah be pleased with him, that the Prophet Interdicted fasting Rajab. We state that this narration is weak. Here, we state that al-'Iz Ibn 'Abd-us-Salaam dispraised those who prevented people from fasting the month of Rajab as cited from him by Ibn Hajar al-Haitami .'
However, some scholars believe that it is disliked to fast during the month of Rajab and al-Hanabila are among them depending on the above-mentioned narration of the Hadeeth of Ibn 'Abbaas, may Allah be pleased with him, about 'Umar, may Allah be pleased with him, asking people to eat and stop fasting in that month. Imaam Ibn Qudaamah said: 'It is disliked to single out Rajab with fasting.'
As for fasting the sacred months, al-Hanaabilah agreed the majority concerning the desirability of fasting during these months. Then, al-Hanaabilah believe if a person leaves fasting one day of Rajab, then the reprehensibility of its fasting is vanished. al-Mirdaawi, may Allah's Mercy be upon him, said: 'It is disliked to single out Rajab with fasting. This is the opinion of Hanbali school, and it is one of the school's issues that are not agreed upon with others.' Then he added: 'We understand from the words of the compiler that it is not disliked to single out any other month except Rajab with fasting, and this is right and there is no disagreement on this point. In other words, reprehensibility is vanished by breaking the fast during Rajab even for one day or by fasting another month of the year.'
Thus, it becomes clear that fasting the month of Rajab is a controversial issue among scholars of Islam and it is not permissible to use it as a reason to produce discord and disputation among Muslims. So, a person can follow the opinion of the majority or the opinion of Hanaabilah. But, fasting some days of Rajab is desirable in the opinion of all scholars without difference and it is not an innovation.
At last, we believe that the opinion of the majority is the dominant one.
Allah knows best.
Fatwa answered by: The Fatwa Center at Islamweb