The prayer of one who is obligated to pray behind one who is praying voluntarily is valid

He also says: I missed the 'Isha' prayer with the congregation in the month of Ramadan. I entered the mosque while the imam was praying tarawih, so I joined him with the intention of praying 'Isha'. When the imam finished the prayer, I stood for the third rak'ah, and the imam had also stood for the prayer, so I completed the next two rak'ahs of the tarawih prayer with him. Thus, I ended up with four rak'ahs in my case. Is this permissible? And is my prayer considered valid in that case?
Answer: What you should have done when he finished the prayer was to stand up and complete your prayer. When he finished the two rak'ahs, you should have stood up and completed your prayer alone, like one who prays with a person and misses part of it; he stands after his imam finishes to complete it. The correct view is that the prayer is valid, and that the prayer of one who is obligated to pray behind one who is praying voluntarily is valid. This is the stronger of the scholars' opinions: that it is permissible for one who is obligated to pray to pray behind one who is praying voluntarily, just as Mu'adh (may Allah be pleased with him) used to pray 'Isha' with his companions, having already prayed it with the Prophet (peace and blessings be upon him), so he would pray with them as a voluntary prayer, while they were obligated to pray.
As for this situation where your imam finished the prayer, and then you stood up and followed him in the last two rak'ahs until you completed four, there is a point of consideration regarding its validity. The closest view, and Allah knows best, is that it is valid, if Allah wills. You do not have to repeat it. This is the closest view, if Allah wills. However, in the future, if something like this happens, the safest course for you is to make up what remains of your prayer alone when he finishes the prayer. Yes.
The presenter: May Allah reward you with good.