Is the specification that is not accompanied by the intention of believing in its فضl (virtue), such as the regular recitation of a specific surah in the sunnah of Maghrib prayer, considered an innovation (bid'ah)? And is it permissible to observe the night of the 15th of Sha'ban or fast on that day based on the weak hadith reported concerning it, out of hope for the potential reward and without believing in its استحباب (recommendation), or is that among the prohibited forms of specification?

If someone dedicates a specific act of worship to a particular time without believing there is a special virtue in performing it at that time, then there is, God willing, no harm in it. It has been reported in the Sunnah that Surah Al-Kafirun and Surah Al-Ikhlas are recited in the two rak'ahs of the Sunnah prayer of Maghrib. As for acting upon a weak hadith concerning the virtues of deeds, it is stipulated that it should not be extremely weak. This does not apply to the hadith about performing Qiyam on the night of mid-Sha'ban, as it is extremely weak; in fact, it has been ruled as fabricated.