What is the ruling on a traveler praying the Maghrib prayer with the congregation with the intention of 'Isha' while shortening it?

Question:
The questioner says: I am a traveler, and I joined a group praying Maghrib. I prayed with them with the intention of the 'Isha' prayer, sat after the second rak'ah, and said the taslim before the imam. What is the ruling?

Answer:
The ruling is that the prayer is not valid. It is obligatory for you to complete it. It is obligatory for you to complete the 'Isha' prayer with four rak'ahs. You prayed with the Maghrib, behind those who are praying Maghrib. It is obligatory for you that when the imam says the taslim, you stand up and perform a fourth rak'ah, because whoever prays behind a resident must complete the prayer. Yes.