Is the prayer of the Imam and the congregants valid if the Imam makes a grave error in reciting the Quran and a congregant corrects him, or must they repeat the prayer? And must a congregant correct a minor error that does not alter the meaning? What is the ruling on the prayer of one who lags behind the Imam by two or more pillars?

Among the pieces of advice for imams is to be open to correction during prayer. If the imam corrects his mistake and completes his prayer, then his prayer is valid, and the prayer of the congregants is valid, and they do not need to repeat it. If a congregant catches the imam while he is bowing and bows with him, then he has caught the rak'ah and the virtue of the congregation. If a congregant lags behind the imam by two pillars or more due to an excuse, if he can catch up with the imam before the next rak'ah, he should do so. Otherwise, he should cancel that rak'ah and make it up after the imam says the taslim, and he does not need to perform the prostration of forgetfulness (sujood al-sahw).