Praying at Night in Ramadaan (Taraweeh)

Bukhari :: Book 3 :: Volume 32 :: Hadith 226

Narrated Abu Huraira:

I heard Allah's Apostle saying regarding Ramadan, "Whoever prayed at night in it (the month of Ramadan) out of sincere Faith and hoping for a reward from Allah, then all his previous sins will be forgiven."