There are three points about fasting the month of Shaban more than other months:
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 the heavens. Thus, Prophet Muhammad liked his deeds to be raised while he was fasting.”
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 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. (Ahmad)
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)
Honor of Ramadan
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)
Fasting Mid-Shaban
It was narrated that ‘Ali ibn Abi Talib said: “The Messenger of Allah said: ‘When it is the night of the middle of Sha’ban, spend its night in prayer and observe a fast on that day. For Allah send an angel to descends at sunset on that night to the lowest heaven and says: ‘Is there no one who will ask Allah for forgiveness, that Allah may forgive him? Is there no one who will ask Allah for provision, that Allah may provide for him? Is there no one who is afflicted by trouble, that Allah may relieve him?’ And so on, until dawn comes.’” (Ibn Majah)