How to Pray Maghrib Behind an Imam Who Is Praying Isha

Q: The brother A. S. H. from 'Uyun al-Jaww says in his question: It is well known that if a person joins the imam in the Isha prayer from the beginning while intending to pray Maghrib, he sits after the third rak'ah, recites the final tashahhud, and waits until the imam says the taslim, then he says the taslim with him. My question, O honorable Shaykh, is: If a person joins the imam after the imam has already prayed the first rak'ah of the Isha prayer, and the person intends to pray Maghrib, does he say the taslim with him on the basis that he has prayed the three rak'ahs that constitute the Maghrib prayer, or what is he required to do? May Allah reward you with good.

A: If a Muslim joins the imam in the Isha prayer after the imam has prayed one rak'ah, and the one who joined has not prayed Maghrib, then what he catches up with the imam suffices for him as the Maghrib prayer, according to the more correct of the two opinions of the scholars. And success is from Allah.