Ruling on the prayer of one who says the closing salam before the imam

The questioner : A person said the closing salam before the imam. He forgot, then remembered after he had sought forgiveness, so he completed the prayer and said the closing salam with the imam. Is his prayer valid or not?
The Shaykh : His prayer is valid and he owes nothing. He was required to perform the prostration for forgetfulness because he said the closing salam before the prayer was completed. However, since he did not miss any part of the prayer with the imam, he owes nothing; because the imam bears the prostration for forgetfulness on behalf of the one praying behind him if he does not miss any part of the prayer.