The ruling on one who joins the imam for the 'Isha' prayer while owing the Maghrib prayer

Question:
He says: Honorable Shaykh, peace be upon you and Allah's mercy and blessings. We are three men who were traveling. Three men, we were traveling, and the time for the 'Isha' prayer came, and we arrived in one of the cities, and they were praying the 'Isha' prayer, while we had not prayed the Maghrib prayer. So some of us joined the imam with the intention of Maghrib, and said the closing salam in the third rak'ah, and completed the fourth rak'ah with the imam. Some of us joined the imam with the intention of 'Isha', then prayed the Maghrib and 'Isha' prayers again afterwards. And some of us joined the imam with the intention of Maghrib, sat down in the third rak'ah, and waited for the imam until he said the salam, then said the salam with him. Please give us a ruling, may Allah reward you, on these matters, and what is required of each of us? And may Allah the Exalted reward us with good?

Answer:
As for the one who comes and the imam is praying the 'Isha' prayer and he has not prayed the Maghrib prayer, and he prays the 'Isha' prayer with him, then prays the Maghrib and 'Isha' prayers afterwards, there is no harm in that. Then the 'Isha' prayer with him is a voluntary prayer, and then he prays the Maghrib and 'Isha' prayers, there is no harm in that, in order to avoid the disagreement among the scholars. And as for the one who prayed the Maghrib with them and sat down in the third rak'ah and said the salam with the imam, there is no blame on him for all of this. And as for the one who said the salam before the imam, he has left what is better, but there is no blame on him, if Allah wills. But if he had been patient until he completed the prayer with them, then prayed the 'Isha' prayer afterwards, that would have been better. If he had been patient, then when his imam said the salam, he said the salam with him, then prayed the 'Isha' prayer afterwards, that would have been the obligatory thing and what is recommended. He does not say the salam; he remains sitting until the imam completes the fourth rak'ah, then he says the salam with him. As for what is better, it is that he prays the 'Isha' prayer with them as a voluntary prayer, then prays the Maghrib prayer alone, and the 'Isha' prayer alone afterwards; because this avoids the disagreement of the scholars who say that the Maghrib prayer behind the 'Isha' prayer is not valid. We ask Allah for success for everyone in that. Yes.