Beginning of Creation

Bukhari :: Book 4 :: Volume 54 :: Hadith 451

Narrated Abu Huraira:

Allah's Apostle said, "When the Imam, during the prayer, says, "Allah hears him who praises Him', say: 'O Allah! Our Lord! All the praises are for You/, for if the saying of anyone of you coincides with the saying of the angels, his past sins will be forgiven."