Verily! we have sent it (this Qur'ân) down In the night of Al-Qadr (Decree). And what will make You know what the night of Al-Qadr (Decree) is?.The night of Al-Qadr (Decree) is better than a thousand months (i.e. worshipping Allâh In that night is better than worshipping Him a thousand months, i.e. 83 years and 4 months). Therein descend the angels and the Rûh [Jibrael (Gabriel)] by Allâh's permission with All Decrees.Peace! (all that night, there is peace and goodness from Allâh to his believing slaves) until the appearance of dawn." Al-Qadr Q97: 1 -5

Narrated By 'Aisha: Allah's Apostle said, "Search for the Night of Qadr in the odd nights of the last ten days of Ramadan." Bukhari, Vol3, Book32, Hadith 234....