the Messenger of Allah said: "Whoever fasts Ramadan and stands (in the night prayer) for it out of faith and seeking a reward (from Allah), he will be forgiven what preceded of his sins. Whoever stands (in the night prayer) on the Night of Al-Qadr out of faith and seeking a reward (from Allah), he will be forgiven what preceded of his sins."
Jami` at-Tirmidhi Book 8, Hadith 2
← Previous Hadith the Messenger of Allah said: "On the first night of the month of Ramadan, the Shayatin are shackled, the jinns are restrained, the gates of the Fires are shut such that no gate among them would be opened. The gates of Paradise are opened such that no gate among them would be closed, and a caller calls: 'O seeker of the good; come near!' and 'O seeker of evil; stop! For there are those whom Allah frees from the Fire.' And that is every night."

Jami` at-Tirmidhi Book 8, Hadith 1 Next Hadith → the Prophet said: "Do not precede the month with a day nor with two days, unless that fast falls on a day that one of you would have (normally) fasted. Fast with its sighting and break fast with its sighting, and if it is cloudy, then count for thirty days, and then break (the fast)."

Jami` at-Tirmidhi Book 8, Hadith 3