The Prophet Muhammad (peace be upon him) said: "Search for the Night of Power (Laylat Al-Qadr) in the odd-numbered nights of the last 10 days of Ramadan." - Sahih Al-Bukhari, Volume 3, Hadith 234
A wife of the Prophet asked him what prayers she should say on Laylat Al-Qadr. The Prophet told her to say: "O God, Thou art forgiving and lovest forgiveness, so forgive me." - Al-Tirmidhi, Hadith 641
"We have revealed this (Quran) in the Night of Power. And what will make you understand what the Night of Power is! The Night of Power is better than one thousand months. The angels and the Spirit (Gabriel) come down with every decree, by the leave of their Lord. That night is the night of peace, till the break of dawn." - The Holy Quran, Chapter 97 (Al-Qadr)
"We revealed this (Quran) in a blessed night (Laylat Al-Qadr); for We wanted to forewarn mankind. In that night every matter is decided wisely." - The Holy Quran, 44:3-4
NOTE: Laylat al-Qadr ("Night of Power" or "Night of Destiny") marks the anniversary of the night on which the Prophet Muhammad (peace be upon him) first began receiving revelations from God through the angel Gabriel. Muslims believe Laylat al-Qadr is one of the last odd-numbered nights of Ramadan. Some Muslims spend the last 10 days of Ramadan in a local mosque. This practice is called "I'tikaf."