The traveler enters with the intention of Maghrib behind those who are praying 'Isha'
Machine translationRead the Arabic original
Question:
The traveler who has not prayed Maghrib comes to a mosque on the way and joins them in the 'Isha' prayer, saying the opening takbir with the intention of Maghrib. Then he stands for the fourth rak'ah. What should he do? Does he say the closing salam, or does he wait?
Answer:
He sits in the third rak'ah. When they say the salam, he says the salam, then he prays 'Isha' after that. He does not stay with them for the fourth rak'ah. If he was ignorant, his prayer is valid; because he was ignorant or forgetful. Yes.
The traveler who has not prayed Maghrib comes to a mosque on the way and joins them in the 'Isha' prayer, saying the opening takbir with the intention of Maghrib. Then he stands for the fourth rak'ah. What should he do? Does he say the closing salam, or does he wait?
Answer:
He sits in the third rak'ah. When they say the salam, he says the salam, then he prays 'Isha' after that. He does not stay with them for the fourth rak'ah. If he was ignorant, his prayer is valid; because he was ignorant or forgetful. Yes.
Source
لقاءات لابن باز - لقاء مع إخوة في الله - ابن باز - ٢ — archive.org (21:31)
The Arabic text is a machine transcription of the audio recording.