Fasting in Sha'ban
Shaban is one of the meritorious months for which we find some particular instructions in the Sunnah of Prophet Muhammad (Pbuh). It is reported in authentic hadiths that Prophet Muhammad (Pbuh) used to fast most of the month in Sha’ban. These fasts were not obligatory on him, but Sha’ban is the month immediately preceding the month of Ramadan. Therefore, some preparatory measures are suggested by the Prophet (Pbuh).
The blessed companion Usama ibn Zaid, (RA) reports that he asked Prophet Muhammad, (Pbuh), “Messenger of Allah, I have seen you fasting in the month of Sha’ban so frequently that I have never seen you fasting in any other month.” Prophet Muhammad (Pbuh) replied: “That (Sha’ban) is a month between Rajab and Ramadan which is neglected by many people. And it is a month in which an account of the deeds of human beings is presented before the Lord of the universe, so, I wish that my deeds be presented at a time when I am in a state of fasting.”
Ummul Mu'mineen 'Aishah (RA), says, “Prophet Muhammad, (Pbuh) would sometimes begin to fast continuously until we thought he would not stop fasting, and sometimes he used to stop fasting until we thought he would never fast. I never saw the Messenger of Allah, (Pbuh) fasting a complete month, except the month of Ramadan, and I have never seen him fasting in a month more frequently than he did in Sha’ban.”
The Prophet (peace and blessings be upon him) used to fast most of the days of Sha`ban, but he used to stop fasting when he got close to the month of Ramadan. That is why Muslim scholars state that fasting is highly recommended in the early part of the month of Sha`ban until few days before the month of Ramadan.
Sheikh Yusuf Al- Qaradawi states:
The Prophet (peace and blessings of Allah be upon him) used to observe fasting in Sha`ban more than he did in other months. This was a kind of self-preparation for the coming of Ramadan; that is, to act as some sort of girding oneself for Ramadan. But there are no textual evidence that there are specific days in Sha`ban in which fasting is commendable. It is, by and large, impermissible for one to prefer certain days to observe voluntary fasting or certain nights to perform Night Prayers, lacking any juristic basis for that action. Religious acts are not left for man’s whims. Rather, they are subject to Divine legislation. Thus, specifying certain times and places for worship and the description of different acts of worship are the matters of the Divine, not that of human.
Fasting in the Second Half of Sha`ban
Fasting in the second part of the month of Sha`ban is a controversial issue among Muslim jurists. According to the Hanbali School, it is makruh (disliked). For the Shafi`i School, it is haram (forbidden). The majority of Muslim jurists state that it is permissible. Hence, it is better for the person to avoid fasting in the second half of the month of Sha`ban unless the person himself is accustomed to fast regular days such as Mondays and Thursdays of every week, or when a person is obliged to make up for missed days of Ramadan before the new Ramadan begins.
Reference: islamonline.net and other sites.