How to Pray Maghrib Behind Someone Praying 'Isha'

Question:
May Allah reward you with good. He says: If I enter the prayer with the imam while he is praying the 'Isha' prayer, intending to pray the Maghrib prayer, what should I do? And what should I do if I miss one rak'ah or more of his prayer?

Answer:
What you should do is pray the Maghrib first, either with those who missed the Maghrib prayer, or by yourself, and then join the congregation for the remainder of the 'Isha' prayer. Do not mix them up by praying Maghrib behind the 'Isha' prayer, for that will cause confusion and difficulty for you. However, if you enter with the imam intending Maghrib while he is praying 'Isha', then when he stands for the fourth rak'ah, you do not stand. Sit down and recite the final tashahhud. If you wish, you may wait until the imam says the taslim and say it with him, or if you wish, you may say the taslim for yourself. Yes.