Night of Power

In Islamic belief, the Laylat al-Qadr (in Arabic: لیلة القدر) or Night of Power is the night when Muslims believe the Quran was first sent down from heaven to the world, and also when the Quran's first verses were revealed to the Islamic prophet Muhammad by the angel Gabriel.
In the Quran, it is said this night is better than 1,000 months (approximate 83.3 years). According to the various hadiths, its exact date is uncertain, but was one of the odd-numbered nights of the last ten days of Ramadan, the ninth month of the Islamic calendar. Since that time, Muslims have regarded the last ten nights of Ramadan as being especially blessed. Muslims believe the Night comes again every year, with blessings and mercy of God in abundance. The surah al-Qadr is named after this Night, and the chapter’s purpose is to describe the greatness of the occasion.
Qadr (قدر) in Arabic, means the measure and limit or value of something or destiny. Some reasons have been offered for its naming:
Other names for this Night include Laylat al-'Azama (Arabic: ليلة العظمة, “Night of the Greatness”) and Laylat ash-Sharaf (Arabic: ليلة الشرف; lit. 'Night of the Honour').
Some Islamic experts believe that the Quran was revealed to Muhammad twice:
The Quran uses the word anzal (انزل) which justifies “immediate revelation”, according to Allamah Tabatabai. Some others believe that the revelation of Quran occurred in two different phases, with the first being its entire revelation on Laylat al-Qadr to the Angel Gabriel (Jibril in Arabic) in the lowest heaven, and then the subsequent verse-by-verse revelation to Muhammad from Gabriel. The first surah revealed were the first seven āyat (verses) of Sūrat al-ʿAlaq ( العلق).
Muhammad would usually practice spiritual retreat (Iʿtikāf) during the last ten days of Ramadan, awaiting the Night of Power, fasting and praying throughout the night, and abstaining from sexual relations. He urged his followers to do the same as one hadith notes: "Whoever stands [in prayer] during the Night of Power out of belief and seeking reward, his previous sins are forgiven." (Sahih al-Bukhari 1901)
The specific date of Laylat al-Qadr is not mentioned in the Quran. Muhammad said God told him the exact date in a dream, but as he went to tell his companions about it, he saw two people fighting and God made him forget the date.
According to the Islamic calendar, an Islamic day begins at Maghrib prayer (sunset). The Night of Power thus spans Maghrib to Fajr prayer the following dawn.
Sunni Muslims believe Laylat al-Qadr is most likely one of the odd-numbered nights among the last ten of Ramadan (i.e., the 21st, 23rd, 25th, 27th, or 29th). Some scholars opine the odd-numbered night falling on a Friday is the year’s Laylat al-Qadr.
Shi’a Muslims similarly believe Laylat al-Qadr to be one of the last ten odd-numbered nights in Ramadan, with the 19th, 21st, and especially the 23rd being most important. The date of 19 Ramadan is the anniversary of Imam ʿAlī’s assassination while praying in the mihrab of the Great Mosque of Kufa, leading to his death on 21 Ramadan.
Shi’a’s say ʿAlī (who is also the fourth Rashidun Caliph to Sunnis) had special insight and intimacy with God on this night. Imam Sadiq is quoted as saying in Tafsir "al-Burhan" (vol. 4, p. 487):
Ibn Abbas was meanwhile aware of both the date and day of the week. Hence, Shi’as have generally concluded it falls on the 23 Ramadan.
According to other hadiths, destinies are written on the night of 19 Ramadan, finalized the night of 21 Ramadan, and ultimately confirmed the night of 23 Ramadan.
Two other possible dates for Laylat-al-Qadr are 27 Ramadan and 15 Sha'ban.
The night is not comparable to any others in view of Muslims and according to a tradition, the blessings due to the acts of worship during this night cannot be equaled even by worshipping throughout an entire lifetime. The reward of acts of worship done in this one single night is more than the reward of a thousand months of worship.
Surah Al-Qadr of the Quran is about Laylat al-Qadr:
Devout Muslims practice spiritual retreat (Iʿtikāf) during the last ten days of Ramadan by staying at a mosque throughout the ten days, awaiting the Night of Power, fasting and praying throughout the night, and abstaining from sexual relations.
Shi'as practice the special prayers (Amaal) of the Night of Qadr every year in mosques, [tekyeh]s, shrines of Imams or children of Imams, Husayniyyas or their own houses. They stay vigilant the whole night until dawn and worship God. The most important practices of the Night of Qadr include congregational prayers, recitation of the Iftitah Supplication, [Abu Hamza al-Thumali] Supplication, and al-Jawshan al-Kabir, and collective supplications while they keep volumes of the Quran on top of their heads. Other rituals of the night include donations of dawn food, payment of their nadhr for the dead, feeding the poor, and emancipation of financial prisoners.
Since the assassination of Ali occurred in the last ten days of the Ramadan month, Shi'as mourn in these nights.