What is the ruling on prolonging prostration behind the Imam?

The prescribed action for the worshiper (ma'mum) is to follow their imam directly, based on the Prophet's (peace be upon him) saying: "Indeed, the imam is appointed to be followed. So when he says 'Allahu Akbar', then say 'Allahu Akbar'. And when he bows, then bow. And when he rises, then rise. And when he says 'Sami'a Allahu liman hamidah' (Allah hears those who praise Him), then say 'Rabbana wa laka al-hamd' (Our Lord, and to You be all praise). And when he prostrates, then prostrate."

Lagging behind the imam and prolonging prostration after he has risen is contrary to the Sunnah, and may lead to the invalidation of the prayer according to some scholars, especially if the worshiper lags behind the imam without a valid excuse until the imam precedes him by a complete pillar. Scholars have clarified that lagging behind the imam is of two types: - Lagging in the pillar: This is when the worshiper delays in following but catches up with the imam in the pillar he has transitioned to. This action is contrary to the Sunnah. - Lagging by a pillar: This is when the imam precedes the worshiper by a complete pillar (e.g., the imam bows and rises before the worshiper bows). The majority of jurists hold that the prayer of the one who lags behind is invalid if the lagging is by the pillar of bowing. However, the stronger opinion is that the prayer is invalid if the worshiper lags behind the imam by a pillar without a valid excuse, whether the pillar is bowing or something else.

Therefore, prolonging prostration behind the imam is either invalidating of the prayer or contrary to the Sunnah, and it must be avoided.