What should the worshipper do if the Imam makes a mistake and does not respond to his reminder?

The action of the ma'mum (follower) regarding the imam's (leader's) forgetfulness varies depending on whether the imam made an addition or omission. In both cases, the ma'mum must alert the imam. If someone knew of the imam's addition and continued with him until he said the tasleem (salutation), their prayer is invalid and they must repeat it. If they only became aware of the addition after the tasleem, their prayer is valid. If the imam intentionally made an addition, his prayer is invalid. However, if he believed it to be valid and his belief did not change upon being alerted, his prayer is valid. If the imam omitted a pillar, such as a bowing (ruku') or a prostration (sujud), the ma'mums must alert him. If he does not return, they perform the pillar themselves, then catch up with him and complete the prayer. If the imam forgets the first tashahhud (testification) and is alerted or remembers before standing up, he must return. If he has already stood up completely, he should not return but should perform the prostration of forgetfulness (sujud al-sahw). The ma'mum follows him, then alerts him to perform the prostration of forgetfulness.