Sahih Bukhari Volume 003, Book 032, Hadith Number 231.
Hadith Section/Book: Sahih Bukhari Sahih Bukhari Book 32. Praying at Night In Ramadhan (Taraweeh)
Narated By Abu Huraira : The Prophet said, "Whoever fasted the month of Ramadan out of sincere Faith (i.e. belief) and hoping for a reward from Allah, then all his past sins will be forgiven, and whoever stood for the prayers in the night of Qadr out of sincere Faith and hoping for a reward from Allah, then all his previous sins will be forgiven."