Laylat al-Qadr (لیلة القدر) (also known as Shab-e-Qadr), basically the Night of Decree or Night of Measures, is the anniversary of two very important dates in Islam that occurred in the month of Ramadan. It is the anniversary of the night Muslims believe the first verses of the Qur'an were revealed to the Islamic prophet Muhammad.
Muslims believe also that this night is when their fate in the following year is decided and hence pray for God all night long and pray for mercy and salvation. This practice is called Ehyaa (basically meaning "revival").
History
Orientalists have contended that prior to Islam, Laylat al-Qadr was the Arab New Year. It was a time when homes were thought to be susceptible to demonic infiltration.. However, there are no references in Islamic traditions to support this claim.
Complete revelation to Muhammad
Laylat Al-Qadr is the anniversary of the night Muslims believe the first verses of the Quran were revealed to Muhammad by the angel Gabriel (Jibril in Arabic). It is also the anniversary of the night in which the Quran is believed by Muslims to have been revealed in its entirety. The Laylat Al-Qadr is also be known as the night of Glory
Sunnah
Muslims often pray extra prayers on this day, particularly the night prayer. They awake, pray, and hope Allah will give them anything they may desire for on this night. Mostly, they perform tilawat (reading the Qur'an). Those who can afford to devote their time in the remembrance of God stay in the mosque for the final ten days of Ramadan. This worship is called itikaf (retreat). They observe fast during the day and occupy themselves with the remembrance of God, performing voluntary prayers and studying the Qur'an, day and night, apart from the obligatory prayers which they perform with the congregation. Food and other necessities of life are provided for them during their stay in the mosque, thus they may not leave the precincts of the mosque except for a genuine religious purpose. Devoting time to remember God, Muslims hope to receive divine favors and blessings connected with the blessed night.
Muhammad was very particular in these regards. It is related that when the last ten days of Ramadan began, he used to keep awake the whole night and was most diligent in worship.
Laylat al-Qadr is to be found in the last 10 nights of Ramadan. There is no history in the Quran as to when the specific date is.
There are some signs reported that muslims should look for. It is not known whether these signs have been reported by individual astronomic observations, however muslims have reported that these signs are present. These signs also help determine the date of the night as there are no reported hadith that mention the exact date of the night. There are different hadith describing when to look for the night. For example:
The Night of Al-Qadr is not specified to one fixed night throughout all the years. Rather, it constantly changes. So one year it could occur on the twenty-seventh night for example and on another year it could occur on the twenty-fifth night, according to Allah's Will and Wisdom. What directs us to this is the Prophet's :saw: saying: "Look for it (i.e. the Night of Al-Qadr) when there remain nine nights, when there remains seven nights, or when there remains five nights (i.e. 21st, 23 rd, and 25th respectively without mention of the 27th)."
According to a book, the following signs are evident
1. The sun rises early in the morning without rays.
2. Rain may fall either during the night or during the day of that night.
3. During night the sky will be lightly foggy.
4. The sky will be slightly lighted without reflections and without rays.
5. The angels and Gabriel all descend down onto earth for many purposes.