Should the congregants follow the Imam if he forgets the middle Tashahhud and stands for the third Rak'ah, then remembers and returns for the Tashahhud?

If a worshiper rises from the first tashahhud then intentionally returns: - The Hanafis, Shafi'is, some Malikis, and Ibn 'Uthaymin are of the opinion that his prayer is invalid. - The Hanbalis and Malikis are of the opinion that his prayer is valid, but the Hanbalis invalidate his prayer if he returns after beginning the recitation of Al-Fatiha, and the Malikis do not invalidate it unless he returns after completing Al-Fatiha.

As for the congregants (ma'mumun): - The Shafi'is are of the opinion that they do not follow the Imam if he returns after having fully stood up. They may either leave him or wait for him. - The Hanbalis are of the opinion that they follow the Imam if he returns before beginning the recitation, but they do not follow him if he has begun it. - The Malikis are of the opinion that it is obligatory to follow the Imam if he returns to sit before completing Al-Fatiha. - Ibn Baz is of the opinion that it is obligatory for the congregants to follow the Imam absolutely, unless they are certain of an error in which following is not permissible, with the Imam performing the prostration of forgetfulness (sujud as-sahw).