Ibn Al Qayyim said:
“There are three points about fasting the month of Shaban more than other months:
Many Benefits of Fasting in Shaban
First: Prophet Muhammad (peace be upon him) 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’ban 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, Prophet Muhammad liked his deeds to be raised while he was fasting.”
What follows are some of the authentic hadiths related to fasting in the blessed month of Shaban.
Deeds are Raised to Allah
Usamah ibn Zaid said:
“I said: ‘O Messenger of Allah, I do not see you fasting any month as much as Sha’ban.’
He said:
That is a month to which people do not pay much attention, between Rajab and Ramadan. It is a month in which the deeds are taken up to the Lord of the worlds, and I like that my deeds be taken up when I am fasting. (An-Nasa’i)
Blessings of Fasting in Shaban
Umm Salamah narrated:
I did not see the Prophet fasting two consecutive months except for Sha’ban and Ramadan. (Tirmidhi)
Aisha (May Allah be pleased with her) reported:
The Prophet Muhammad did not observe voluntary fasting so frequently during any other month as he did during Sha’ban. He observed Saum throughout the month of Sha’ban.
In another narration, she says:
He observed Saum during the whole month of Sha’ban except a few days. (Al Bukhari and Muslim)
Prophet Muhammad said:
Do not precede Ramadan by fasting the day or two before it. (Bukhari and Muslim)
Making Up the Missing Fasts
Aisha narrated:
I would not make up what was due upon me from Ramadan except in Sha’ban, until the Messenger of Allah died. (Tirmidhi)
She said in another narration:
If I had some part of the fast of Ramadan to make up, I would not be able to atone for it except in Sha’ban. (Abu Dawud)
Aisha reported:
If one amongst us had to break fasts (of Ramadan due to natural reasons, i.e. menses) during the life of the Messenger of Allah she could not find it possible to complete them so long she had been in the presence of Allah’s Messenger till Sha’ban commenced. (Muslim)
Honor of Ramadan
It was narrated in a weak hadith that Anas narrated that:
The Prophet was asked which fast was most virtuous after Ramadan?
He said:
Sha’ban in honor of Ramadan.
He said: “Which charity is best?”
He said:
Charity in Ramadan. (Tirmidhi)
SOURCE: https://aboutislam.net/reading-islam/about-muhammad/the-many-benefits-of-fasting-in-shaban/