Ruling on the prayer of one who omits the prostration for forgetfulness

Question:
He says: If the number of units of prayer is increased, or if something is decreased from that, and one does not perform the prostration for forgetfulness, is the prayer invalid?

Answer:
This requires a detailed explanation: If one intends to omit the prostration while he is in prayer, this is if he does so deliberately, and he is one who knows the legal ruling; his prayer is invalid. But if he is ignorant, or forgetful; his prayer is not invalid, his prayer is valid.
As for if he completed the prayer with the intention of performing the prostration for forgetfulness, then he forgot it, or he deliberately omitted it after that, after he had said the closing salam; his prayer is valid, and he commits a sin by omitting the prostration for forgetfulness which is obligatory upon him; because it is a complement to his prayer, and his prayer is not invalidated by it; because he completed it with the salam, and this prostration is obligatory upon him to complete the prayer. If he prostrates; that is what is obligatory upon him, and if he does not prostrate; he has sinned, and his prayer is valid, and he is sinful.
As for if he omitted it in a state of forgetfulness, or out of ignorance of the legal ruling; he owes nothing.

The presenter : May Allah reward you with good.