The Prayer of the Congregation Behind an Imam Who Deliberately Adds a Rak'ah

The questioner:
Honorable Shaykh, may Allah grant you success. He says: Is the prayer of the congregation valid behind an imam who deliberately added a rak'ah to the prayer after they had already recited the tashahhud with him, and he did not sit?

The Shaykh:
They should not follow him. If they do not follow him, their prayer is valid. However, if they follow him while knowing that it is an extra rak'ah and that it is not permissible to follow him in that, their prayer is invalid, because they added it deliberately. Yes.

The questioner:
Honorable Shaykh, may Allah grant you success.

The Shaykh:
Therefore, they say: If he persists and is not certain of his own correctness, if he persists and does not return, and they have recited the tashahhud with him, and he has not been certain of his own correctness, his prayer is invalid, and the prayer of those who followed him knowingly is invalid, not if they were ignorant or forgetful. Yes.