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

Q: What is the ruling on saying the closing salam before the imam in a state of forgetfulness? Is the prayer valid or not?

A: If the one praying behind the imam says the closing salam before the imam due to forgetfulness and then realizes it, he should return to his intention of prayer, then say the closing salam after his imam. He owes nothing, and his prayer is valid, unless he is one who joined the prayer late. If he is late by one unit of prayer or more, he should perform the prostration for forgetfulness after making up the units of prayer he owes, on account of his saying the closing salam before the imam due to forgetfulness.