Narrated Abu Huraira: Allah's Apostle said: "Whoever establishes prayers during the nights of Ramadan faithfully out of sincere faith and hoping to attain Allah's rewards (not for showing off), all his past sins will be forgiven."
Hadith ReferenceSahih Bukhari / The Book of Belief (Faith) / Hadith: 37
Hadith Gradingمحدثین:أحاديث صحيح البخاريّ كلّها صحيحة