What is the religious ruling on someone who said the salam before the imam?

If the Imam is preceded in the pillars of prayer intentionally—including the salām—the prayer is invalidated. However, if it is done out of forgetfulness, it is not counted, and the follower must continue with his Imam. If he does not return to his position until the Imam catches up with him, his prayer becomes invalid. As for intentionally preceding the Imam in the takbīrat al-ihrām (the opening takbīr), this invalidates the prayer from its very beginning. It is obligatory for the follower to properly follow the Imam and to have presence of mind in prayer.