Praise be to Allah.
It is not prescribed in Islam to celebrate the 15th of Sha‘ban, whether that is by spending the night in prayer, dhikr and reading Quran, or by distributing sweets or giving food to people and so on.
It is not known in the sahih Sunnah that this night is to be singled out for acts of worship or customs.
The night of the fifteenth of Sha'ban is just like any other night.
The scholars of the Standing Committee for Issuing Fatwas said:
“It is not permissible to celebrate the occasion of Laylat al-Qadr or any other night, or to hold celebrations on other occasions such as the night of the fifteenth of Sha'ban, the night of the Mi'raj , or the Prophet’s birthday (Mawlid) and so on, because these are innovations that have been introduced into the religion and were not narrated from the Prophet (blessings and peace of Allah be upon him) or any of his Companions. And he (blessings and peace of Allah be upon him) said: “Whoever does an action that is not part of this matter of ours (i.e., Islam) will have it rejected.” And it is not permissible to help others to hold these celebrations by giving money or gifts or distributing cups of tea, and it is not permissible to give speeches and lectures on these occasions, because that comes under the heading of approving of them and encouraging them. Rather it is obligatory to denounce them and not to attend them.” (Fatawa al-Lajnah ad-Daimah, 2/257-258)
Shaykh Ibn ‘Uthaymin (may Allah have mercy on him) was asked:
We have some customs that we grew up with and that have been passed down to us, on some occasions, such as making cakes and cookies on ‘Eid al-Fitr , and preparing platters of meat and fruit on the night of the twenty-seventh of Rajab and the fifteenth of Sha‘ban, and different kinds of sweets that must be prepared on the day of ‘Ashura. What is the Islamic ruling on that?
“As for expressing joy and happiness of the days of ‘Eid al-Fitr and ‘Eid al-Adha, there is nothing wrong with that if it is within the limits prescribed in Islam, such as preparing food and drink and the like. It is proven that the Prophet (blessings and peace of Allah be upon him) said: “The days of at-Tashriq are days of eating and drinking and remembering Allah, may He be glorified and exalted.” This refers to the three days following ‘Eid al-Adha, when the people offer their sacrifices and eat from the meat and enjoy the blessings that Allah has bestowed upon them. Similarly, on ‘Eid al-Fitr there is nothing wrong with expressing joy and happiness so long as it does not overstep the limits set by Islam.
As for expressing joy on the night of the twenty-seventh of Rajab or the fifteenth of Sha‘ban or the day of ‘Ashura , this is something for which there is no basis. Rather it is forbidden and the Muslim should not attend if he is invited to such celebrations. The Prophet (blessings and peace of Allah be upon him) said: “Beware of newly invented matters, for every newly invented matter is an innovation (bid‘ah), and every innovation is a going astray.”
The night of the twenty-seventh of Rajab is what some people claim is the night of the Mi'raj during which the Messenger (blessings and peace of Allah be upon him) was taken up to Allah, may He be glorified and exalted. There is no proof of this date from a historical point of view, and everything for which there is no proof is false, and that which is built on falsehood is also false. Even if we assume that this event took place on that night, it is not permissible for us to introduce on that date any of the symbols of festivals or acts of worship, because no such thing is proven from the Prophet (blessings and peace of Allah be upon him) or from his Companions who were the closest of people to him and the keenest of people to adhere to his Sunnah and follow his path. So how could it be permissible for us to introduce something that did not happen at the time of the Prophet (blessings and peace of Allah be upon him) or at the time of his Companions?
Even with regard to the night of the fifteenth of Sha'ban, there is no proof that the Messenger (blessings and peace of Allah be upon him) ever venerated it or spent that night in prayer. Rather some of the Tabi'in spent that night in prayer and dhikr, not in eating and celebrating as if it were a festival.” (Fatawa Islamiyyah, 4/693)
And Allah knows best.