What is the criterion for following the Imam? And does the worshipper follow the Imam if he adds or omits a pillar, or adds or omits an obligatory act, or adds or omits a Sunnah, or should he intend to separate from the congregation?

The congregant must follow the Imam in all actions of the prayer, and it is not permissible for him to precede him or align with him, as the Prophet (peace be upon him) said: "Indeed, the Imam is appointed to be followed."

- If the Imam intentionally or unintentionally omits the opening takbeer (Takbeerat Al-Ihram): His prayer is not valid, and following him is not permissible. - If the Imam omits a pillar that cannot be remedied (such as reciting Al-Fatihah or tranquility): The congregant should intend to pray individually and complete his prayer. - If the Imam unintentionally omits a pillar that can be remedied (such as bowing or prostrating): The congregants must alert him, and he must return to remedy the pillar unless he has reached its position in the next rak'ah. In that case, the first rak'ah is canceled, and the second one takes its place. - If the Imam omits a pillar that the congregant believes in, but the Imam does not, or if he does something forbidden according to the congregant but not to him: The prayer behind him is valid. - The congregant should follow his Imam in matters where ijtihad (independent reasoning) is permissible, even if he differs with him in his ruling. - If the Imam unintentionally adds a pillar: He must be alerted. If he does not return, the congregant is not allowed to follow him, and he must remain seated and complete his prayer individually. If he follows him knowingly, his prayer is invalidated. If he was ignorant or forgetful, his prayer is valid. - If the Imam unintentionally omits a necessary obligation of the prayer (such as the first tashahhud): The congregant must not stop following him, and he must be alerted. If he remembers it before leaving its place, he should perform it. If he remembers it after leaving its place but before the next pillar, he should return and perform it, and then perform the prostration of forgetfulness (sujood al-sahw). If he remembers it after reaching the next pillar, the obligation is dropped, and he should continue and perform the prostration of forgetfulness. - If the Imam omits a sunnah (recommended act) of the prayer: There is no consequence for him or for the congregants. - Anything that is considered a divergence from the Imam must be abandoned by the congregant, except for what does not entail an actual divergence in action, such as raising the hands.