[URL="http://islamqa.info/en/ref/13726"]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.
Abu Hurayrah (may Allah be pleased with him) reported that the Messenger of Allah (peace and blessings be upon him) said: “When Sha`ban is half over, do not fast.”(Classed as authentic by Al-Albani)