The wisdom of fasting Sha’baan more than other months:
Ibn Al Qayyim, may Allah have mercy on him, said in Tahtheeb As-Sunan,
“There are three points about fasting the month of Sha’baan more than other months:
First: the Prophet, used to fast three days every month. Perhaps he was busy and could not fast in some months, so he gathered all these in Sha’baan to fast them before the obligatory fast.
Second: he may have done so to honor Ramadan. This fast is similar to the regular voluntary prayers before the obligatory ones to honor them.
Third: it is a month when deeds are raised to Allah The Almighty. Thus, the Prophet, liked his deeds to be raised while he was fasting.”
Ibn Hajar seconded this last opinion. He said, "Priority is given here to a more authentic Hadeeth which is: it was narrated on the authority of Usaamah ibn Zayd that he inquired, ‘"O Messenger of Allah, I never find you fasting in any month like you do during the month of Sha’baan."The Prophet said:"That is a month that 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 my deeds to be raised while I am fasting."’ [An-Nasaa’i and Abu Daawood] [Ibn Khuzaymah: Saheeh]
A similar narration was narrated by ’Aa’ishah on the authority of Abu Ya‘la where the Prophet, said: “Allah writes the names of those who are to die during the course of the year. So, I would rather not record my name except while I am fasting.”
How is it that the Prophet, , did not fast frequently in Muharram, despite the fact that he said: "it is the best fast" and he encouraged fasting in Sha’baan?
This confusion was resolved by An-Nawawi and narrated by Ibn Hajar . He said, "Perhaps the Prophet, did not know this except by the end of his life; so, he was not able to fast a lot in Muharram. The other possibility is that he had many excuses such as travelling and illness, for example, which prevented him from fasting frequently in it."
Ibn Rajab adopts the view that fasting in Sha’baan is better than Muharram because of the Hadeeth (narration) by At-Tirmithi who said, "Fasting in Sha’baan resembles the regular voluntary prayers before or after the obligatory ones. On the other hand, when the Prophet, sallallaahu ‘alayhi was sallam, said: ‘The best fast after Ramadan is the month of Allah; Al-Muharram’, he meant voluntary fasting in general. However, the virtue of the fasting that precedes and follows Ramadan is narrated thereto. It falls between two great months, the forbidden month and the month of fasting. There might be something better than that whose virtue is known; either in general or for a certain privilege." [Al-Lataa’if]
Another virtue:
Another virtue is mentioned about Sha’baan. Mu‘aath ibn Jabal, may Allah be pleased with him, narrated that the Prophet, said: “On the night of mid-Sha’baan, Allah looks at His creation and forgives all of them except for the polytheist and the quarrelsome." [At-Tabaraani] [Al Albaani: Saheeh]
A final say about the night of mid-Sha’baan:
Shaykhul-Islam said (Al-Fataawa Al-Misriyyah), "The night of mid-Sha’baan has virtues. Some predecessors used to perform Qiyaam (voluntary night prayer) on it. However, gathering in mosques to revive it is a religious innovation. Rather, they used to pray in their houses like the usual Qiyaam night prayers. If some people gather to pray on this night as well as other nights without constantly doing so, there is no harm for the Prophet, led Ibn ‘Abbaas and Huthayfah in prayer. The ruler should prohibit these innovated gatherings." Ibn Rajab said, "This is the opinion adopted by Al-Awzaa‘i, the Imaam, jurist and scholar of the people of Shaam. It is the most correct opinion, Allah willing."
Concerning the Hadeeth: "When the middle of Sha’baan comes, do not fast" which was narrated by Ahmad, Abu Daawood, An-Nasaa’i and Ibn Maajah, it is a Munkar Hadeeth and classed as weak by Ibn Mahdi, Ahmad, Abu Zur‘ah and Al-Athram . It was narrated by Ahmad for the Hadeeth in which the Prophet, says: "Do not precede Ramadan by fasting the day or two before it." However, what is understood from the Hadeeth is that it is permissible to fast two days before Ramadan. At-Tahaawi believes that it is abrogated. In any case, there was a consensus to abandon acting upon it. Regarding the day of mid-Sha’baan, it is not prohibited to fast on it, as it one of the White Days.