Praise be to Allaah. 

There is no saheeh marfoo’ report that speaks of the virtue of the middle of Sha’baan that may be followed, not even  in the chapters on al-Fadaa’il (chapters on virtues in books of hadeeth etc.). Some maqtoo’ reports (reports whose isnaads do not go back further than the Taabi’een) have been narrated from some of the Taabi’een, and there are some ahaadeeth, the best of which are mawdoo’ (fabricated) or da’eef jiddan (very weak). These reports became very well known in some countries which were overwhelmed by ignorance; these reports suggest that people’s lifespans are written on that day or that it is decided on that day who is to die in the coming year. On this basis, it is not prescribed to spend this night in prayer or to fast on this day, or to single it out for certain acts of worship. One should not be deceived by the large numbers of ignorant people who do these things. And Allaah knows best.

Shaykh Ibn Jibreen.

 If a person wants to pray qiyaam on this night as he does on other nights – without doing anything extra or singling this night out for anything – then that is OK. The same applies if he fasts the day of the fifteenth of Sha’baan because it happens to be one of the ayyaam al-beed, along with the fourteenth and thirteenth of the month, or because it happens to be a Monday or Thursday. If the fifteenth (of Sha’baan) coincides with a Monday or Thursday, there is nothing wrong with that (fasting on that day), so long as he is not seeking extra reward that has not been proven (in the saheeh texts). And Allaah knows best.