All perfect praise be to Allah, The Lord of The Worlds, and may His peace and blessings be upon our Prophet Muhammad and upon all of his family and companions
The majority of the Hanafi, Maliki,Shafie, in addition to some Hanabali jurists, are of the view that fasting the month of Rajab is recommended and the same goes for the rest of the sacred months: Muharram, Dhul-Qidah and Dhu al-Hijjah. This view is based on some narrations, such as: When the Prophet (PBUH) was asked about the reason of fasting the month of Sha’baan. He said (What means): "That is a month to which people do not pay much attention, between Rajab and Ramadan.” [An-Nissa’ee/pp.2357]. According to scholars, this narration proves that Rajab and Ramadan are months of worship and people should pay more attention to them.
However, there are many weak narrations in this regard, such as the one stated by Al-Hafid Ibn Hajar: the Messenger of Allah said (PBUH): "Fast three days during the sacred months and omit fasting for three days alternately." They (jurists) added: "A person is recommended to perform righteous deeds based on weak narrations, in this regard, and should be aware of the fake narrations that shed light on the virtue of the month of Rajab."
Furthermore, Ibn Hajar Al-Haythami (May Allah have mercy on his soul) stated (What means): "There are many fake narrations stressing the virtue of fasting the month of Rajab, yet Muslim jurists are of the view that observing fast during this month is recommended based on other weak narrations because they encourage offering righteous deeds during this month.” [Al-Fatawa Al-Fiqhiaa Al-Kubra vol.2pp.54].
Lately, according to some righteous companions who had similar opinions in this regard, Hanbali’s doctrine has adopted their famous fatwa which states: "Fasting the month of Rajab solely is reprehensible because people will assume that it is an obligation like Ramadan.”
This is based on what was narrated by Ibn Abi Shyba that Al-Khrash Ibn Al-Hu’r said (What means): ”I saw Omar hits fasting people who observe fasting excessively during Rajab on their hands over and over until they put them in the cooking cauldron and says: eat, since this month used to be glorified by the people of the age of ignorance.” [Al-Moghni vol.3 pp.53] for Ibn Qhoddama.
The reason behind Omar Ibn Al-Khatab`s (May Allah be pleased with him) reaction is that people will assume that fasting Rajab is an obligation similar to Ramadan, so he adopted this Sharia policy to convince them otherwise.
Therefore, Hanbali jurists (May Allah have mercy on their souls) stated: "The aforementioned reprehensibility can be removed by abstaining from fasting for one day during the month of Rajab or by fasting an entire month in addition to Rajab in order to avoid fasting the latter month solely."
Consequently, there is no harm on whoever used to make voluntary fast and increased days of fast during Rajab in order to get the whole reward according to the four doctrines. And Allah the Almighty Knows Best.