Does the ruling on catching a rakʿah in congregational prayer—by remaining with the imam for the duration of one tasbīḥah—apply to all rakʿahs or only to the first rakʿah? And is completing the recitation of Al-Fātiḥah in the subsequent rakʿahs before bowing considered an act of extremism?

A rak'ah is attained by performing rukūʿ (bowing) with the imam. If a worshiper intentionally lags behind his imam until the imam precedes him by one pillar, his prayer becomes invalid according to some scholars. The Hanbalis hold that whoever catches the rukūʿ with the imam has attained the rak'ah, even if he did not attain the measure of ṭuma'nīnah (tranquility) with him; it is sufficient that he himself attains ṭuma'nīnah. They also do not obligate the recitation of al-Fatihah upon the worshiper in any circumstance.

Thus, if the imam bows while the worshiper is reciting al-Fatihah, the worshiper should interrupt his recitation and follow the imam, because following the imam is obligatory, while reciting al-Fatihah for the worshiper is considered sunnah (recommended) by them. However, the more preponderant opinion is that reciting al-Fatihah is obligatory for the worshiper. If the imam bows before the worshiper completes it, the worshiper should complete it, even if the imam raises (from rukūʿ), unless the imam has preceded him by three intentional pillars. Adding an extra rak'ah to the prayer invalidates it, but one who is ignorant of the ruling is excused and is not required to repeat past prayers.