Some virtues of the night of 15th of Shaban.
Prophet Muhammad(Peace and Blessings of Allah be upon him) said: "Allah Almighty looks upon all those created by Him in the middle Night of Sha'ban and forgives all those created by Him, except the one who associates partners with Him or the one who has malice in his heart (against a Muslim)". [Saheeh Ibn-e-Habban, vol 7, p470]
Aishah (RadiAllah) narrates: ‘One night that the RasulAllah was staying in my house, I did not find him at home. I left my house in search for him and found him (the Prophet) at Jannatul Baqi (the graveyard of Madinah Munawarrah). The Prophet stated: Aishah, did you feel that Allah and His Prophet would wrong you?’ I (Aishah) then said: ‘O! RasulAllah, I thought that you had gone to another of your wives.’ He said: ‘Allah turns His special attention towards the 1st Heaven on this night and forgives the number of His servants as much as are the hairs on the sheep of Bani Kalb.’ (Jami Tirmidhi, p156)
Kalb was a big tribe the members of which had a very large number of sheep. Therefore, the last sentence of the Hadith indicates the big number of the people who are forgiven in this night by Allah Almighty.
A similar narration in Sunan Baihaqi from Aishah (RadiAllah) wherein she also relates further: ‘The Prophet returned home and began to perform Salah. The Prophet fell into Sajdah and performed such a long Sajdah that I had feared he had passed away. When I saw this, I moved from my bed and moved his thumb. The thumb moved and I returned to my place. When the Prophet had finished Salah he stated: ‘Jibrail came to me and said that tonight is the middle night of Sha’ban (15th) and in this night Allah will forgive so many people from the Hellfire, as much as are the hairs on the sheep of Bani Kalb. However, there are certain unfortunate individuals who will not be forgiven, even in this night. Those who join partners with Allah , those who have enmity for their brothers, those who break the ties of kith and kin, those men who keep their lower garment below their ankles, those who disobey their parents and those who habitually drink alcohol.’ (Sunan Baihaqi/ At-Targeeb, vol2, p232)
Nafl Fast on the following Day
Sayyidina Ali (RadiAllah) narrates RasulAllah (PBUH) said: ‘When the 15th night of Sha’ban comes, on that night busy yourself in worship and keep a fast during the day, for in that night, soon after sunset, the special mercy of Allah descends to the first Heaven and He proclaims, ‘Is there any servant of Mine who begs forgiveness from Me that I may forgive him? Is there a servant of Mine who begs sustenance from Me that I may grant him sustenance? Is there a servant of mine in distress who asks for good health and well-being from Me that I may bestow good health and well-being upon him?’ In the same manner, Allah (SWT) calls different kinds of needy people to supplicate to Him for their needs at that time so that he may grant their supplications until the daybreak.’ (Sunan Ibn Majah, p99/ At-Targeeb, p310)