It is recommended to fast most of the eighth month of Sha'aban. 'Aisha (raa) related: "I have never seen the Prophet (saas) complete the fasting of a month at all, except the month of Ramadan. I have never seen him fast most of a month, except Sha'aban." (Bukhari/Muslim)
The hadith indicates the Prophet's Sunnah in preparation for the month of Ramadan is fasting most of the eighth month, Sha'aban, in anticipation of Ramadan. Thus, the believer may fast during Sha'aban as much as he or she pleases, the more the better.
The hadith in question is reported by Osamah Bin Zaid (raa) who asked the Prophet (saas): "O Messenger of Allah, why don't you observe fast in other months as you do in Sha'aban?'' The Messenger responded: `This is a month most people neglect, between Rajab and Ramadan, the month in which (the annual deeds of humanity) are raised to the Lord of the worlds. So, I want my deeds to be raised while I am observing fast'" (Abu Dawud, and Ibn Khuzaimah) This Hadith is not authentic, for it contradicts a verse in Al-Qur'an, according to many scholars. They stated Allah (SWT) said: "We sent it down during a blessed night, for We (ever) wish to warn against evil. In that night is made distinct every affair of wisdom." (Al-Qur'an, 44-3)
This is the Night of Power (Lailatul Qadr), the night in which the deeds of humanity are returned and the decrees for the following year are announced to the angels, not as the above hadith alleged. The Qur'anic commentators said: On this night, Allah will decree and explain what will take place in the affairs of humanity and the world, their earnings, longevity, who will live or die, what type of deeds, good or bad, virtues or non-virtues and what type of work. Allah (SWT) will reveal from the protective slate, Lawhul-Mahfuz the record of every living being to the Angels as the annual records are being raised and stored away.