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....

Narrated By 'Ubada bin As-Samit: The Prophet came out to inform us about the Night of Qadr but two Muslims were quarreling with each other. So, the Prophet said, "I came out to inform you about the Night of Qadr but such-and-such persons were quarreling, so the news about it had been taken away; yet that might be for your own good, so search for it on the 29th, 27th and 25th (of Ramadan). Bukhari, Vol3, Book32, Hadith 240.