"As for what is authentic regarding the night of the 15th of Sha'bân, then the Prophet (peace be upon him) said:
"Allâh, the Blessed and Exalted, comes to His Creation on the 15th night [laylat un-nisf] of Sha'bân, and He forgives all of His Creation, except for the polytheist and the one who has animosity towards other Muslims [al-mushâhin]."
It is an authentic narration narrated by a number of Companions with a number or different chains that strengthen each other by way of Mu'âth ibn Jabal, Abű Tha'labah al-Khushanî, 'Abdullâh ibn 'Amr, Abű Műsâ al-Ash'arî, Abű Hurayrah, Abű Bakr as-Siddîq, 'Awf ibn Mâlik, and 'Â'ishah…
(…What follows here in the Arabic is a long, 4-page discussion by al-Albânî of the different chains of the narration.To summarize what he said, different wordings of the narration can be found in 'as-Sunnah' of Ibn Abî 'Âsim, 'Sahîh Ibn Hibbân,' 'Shu'ab al-'Îmân' of al-Bayhaqî, 'al-Mu'jam al-Kabîr' and 'al-Awsat' of at-Tabarânî, the 'Musnad' of al-Imâm Ahmad, the 'Sunan' of Ibn Mâjah, the 'Musnad' of al-Bazzâr, and many others, on the authority of the eight mentioned Companions.)
…So in summary, the narration is authentic without a doubt, as authenticity could be established for it even if there were not so many routes, so long as they are free of any severe weaknesses, as is the case with this narration."
[end quote - from 'Silsilat ul-Ahâdîth as-Sahîhah' #1145]
This hadîth shows us the virtue of the 15th night of Sha'bân, and as Shaykh al-Albânî said in his checking of 'Islâh Al-Masâjid' (p.99): "The authenticity of this hadîth does not necessitate taking this night as an occasion to gather with the people and perform acts of innovation like those the author mentioned…" He is referring to people illuminating the masâjid, praying 100 rak'ahs, reciting Sűrat al-Ikhlâs ten times in each rak'ah, etc. from the things mentioned by al-Qâsimî, the author of 'Islâh al-Masâjid.'
So, the point is: to specify this night as a night for specific acts of worship is what is to be considered an innovation in the Religion, while we are to acknowledge full well the virtue of this night, as indicated by the above mentioned authentic hadîth – as opposed to what is assumed by some who are overly zealous in protecting the Sunnah and preventing the practice of innovation, that the 15th of Sha'bân has no importance - and Allâh Knows best.