What is the ruling on the action of the Imam and the congregants after he was informed of forgetting a prostration in the last rak'ah of the Asr prayer, where the Imam performed the prostration of forgetfulness (sujud al-sahw) and then the prayer was repeated again?

If the Imam is certain that he did not omit a prostration, he should not pay attention to what a single congregant says. A congregant's claim that the Imam omitted a prostration does not affect the validity of the Imam's prayer or the prayer of the other congregants. As for the congregant who believes the prostration was omitted, he must alert the Imam. If the Imam does not respond, he must perform the prostration himself and not follow the Imam in omitting it. If he follows the Imam in omitting it, his prayer is invalidated if he was aware of the ruling. If he was ignorant, it is considered that he rectified the prayer before a long separation occurred.