The ruling on one who catches the 'Isha' prayer while owing the Maghrib prayer

Question:
As for the questions, as you can see, there are many, and perhaps we will select from them. A questioner says: I came from al-Madinah al-Munawwarah to Jeddah, and Maghrib was approaching while I was on the road. I arrived in Jeddah and entered the mosque, and I found them performing the iqamah for the prayer, the 'Isha' prayer. What must I do?

Answer:
We begin by saying that you must pray Maghrib first. You pray Maghrib first, then you pray with them whatever remains of 'Isha', because the order is obligatory between the prayers. If you wish, you may join them with the intention of Maghrib while they are praying 'Isha'. If you join them with the intention of Maghrib, then when they reach the fourth rak'ah, you sit and perform the final tashahhud. Then, if you wish, you may say the taslim for yourself, or if you wish, you may wait and say the taslim with the imam. That will have fulfilled your Maghrib. Then you stand up after that and come to the prayer of