The ruling on a latecomer following the imam if the imam adds a rak'ah to his prayer

Question:
'Awad is with us on the line, please, my brother 'Awad. Peace be upon you and Allah's mercy and blessings. And upon you be peace. Peace be upon you and Allah's mercy. I say: An imam, may Allah bless you, led the congregation in a four-rak'ah prayer. After he finished the first rak'ah, a group came and joined him in the second, third, and fourth rak'ahs. The imam stood up and did not sit for the final tashahhud, and he performed a fifth rak'ah. The group that had come split into three groups. Two groups stood up with the imam and completed the fifth rak'ah with him; this was the fifth rak'ah for the imam and the previous congregation, but the fourth in number for them. When they prostrated in sujud al-sahw, the imam said the taslim, and one group said the taslim with him. Two groups stood up: the group that had not stood up with the imam for the fifth rak'ah because they knew the imam had made a mistake, and they performed their fourth rak'ah in number. Which of these groups has a valid prayer? Thank you.

Answer:
Well, my brother, the answer is summarized in two points. Those who stood up with the imam without knowing that it was an extra rak'ah have a valid prayer, because they did not intend the addition, or they were ignorant and thought they were required to follow him even if it was extra; if they thought that, their prayer is also valid, and they are excused due to ignorance. As for the latecomers, they do not count the extra rak'ah; they do not count the extra rak'ah, but rather they pray four rak'ahs: what they caught up with the imam and what they missed, which they complete after the imam. Yes.