When the Imām says amen, you too say amen, for whoever says amen at the same time the angels say amen will have his previous sins forgiven

Abu Hurayrah (may Allah be pleased with him) reported that the Prophet (may Allah's peace and blessings be upon him) said: "When the Imām says amen, you too say amen, for whoever says amen at the same time the angels say amen will have his previous sins forgiven."