Q: A disagreement occurred between
a group of followers in congregation because the Imam (the one who leads congregational Prayer) mistakenly performed a fifth rak`ah in a four-rak`ah prayer. Some of them kept sitting until the Imam rose up and performed the additional Rak`ah (unit of prayer) and then followed him when he said Tashahhud (a recitation in the sitting position in the second/ last unit of Prayer) and Taslim (salutation of peace ending the Prayer). Others, although they knew that it was an extra rak`ah, followed him.
Some who were doubtful concerning the extra Rak`ah followed him. We would like that your eminence, give us your legal opinion concerning what should the followers do in such-like situation in the future? May Allah guard you!
If any follower knew that the Imam was about to [mistakenly] offer an extra Rak`ah, for example a fifth Rak`ah in a four-Rak`ah prayer, he should say out loud, 'Subahan Allah (All glory is due to Allah)' so that the Imam would not continue performing it. If the Imam continued, in such case the follower should sit and wait for the Imam then say Taslim after the Imam says it. Therefore, the prayer of those who (Part No. 7; Page No. 133) waited for the Imam then followed him when saying Taslim is correct. As for those who rose up and followed the Imam although they knew that it was an extra Rak`ah and knew the legal ruling (i.e. they should not follow the Imam), their prayer would be Batil (null and void) for they should not have followed the Imam and therefore have to repeat their prayer. One who thought that the prayer was incomplete or doubted whether there was an increase or not (in the action of prayer) should follow the Imam to complete his prayer with him. Therefore, the prayer of one who rose up with the Imam while in doubt [as regards the actual number of already offered Rak`ahs] is correct; same is the case with those who thought that their prayer was incomplete and accordingly rose up to complete it with the Imam.May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.