What is the ruling on the prayer of a congregant who forgot to bow with his imam and did not realize it until the imam was prostrating, so he prostrated with him without bowing, and what is the ruling on his prayer if he forgot to rise from bowing with the imam and prostrated with him from a bowing position?

If a person is delayed in following the Imam due to an excuse, missing one or more pillars (rukn), they must perform what they missed and then continue following their Imam, and there is no blame upon them. However, if the delay is without an excuse, their prayer becomes invalid if they fall behind by a complete pillar.

If a congregant forgets a pillar, such as bowing (ruku') or rising from it, and only realizes it after the Imam has already moved to the next pillar and prostrated with him without performing the missed pillar, then that particular rak'ah (unit of prayer) is invalidated for them. They must perform another rak'ah after the Imam says the salām (final greeting) and then perform the prostrations of forgetfulness (sujood as-sahw) after the salām. If they do not perform the rak'ah and instead say the salām with the Imam, their prayer is invalidated and they must repeat it.