What is the ruling on the prayer of the followers if they hear a prostration verse and prostrate while the imam is bowing and has not prostrated?

Question:
May Allah reward you with good and do you well. Our brother says: In one of the obligatory prayers, when we were praying Maghrib, the imam recited Surat al-Hujurat. When he finished it, he said the takbir and bowed, while a number of the worshippers in the back rows thought it was a prostration verse, so they prostrated. They did not rise from the prostration until the imam said the takbir and rose from the bowing. What is the ruling on what they did? Is their prayer valid?

Answer:
Their prayer is valid if they performed the bowing afterwards. When they realized that he had not prostrated, they rose from the prostration, performed the bowing, and caught up with the imam. Their prayer is valid because they are excused due to their lagging behind him. However, if they did not perform the bowing and caught up with the imam in the rest of the prayer, and did not perform the bowing they left, then if they remember it soon while they are still in their place, they perform a complete rak'ah in place of the rak'ah from which they left the bowing, then they prostrate for forgetfulness and say the taslim. If a long time has passed and they did not know until later, they repeat the prayer in its entirety.