Is it valid for a traveler to shorten the 'Isha' prayer if he prays it behind someone who is praying Maghrib?

Question:
May Allah reward you, Honorable Shaykh. This questioner says: I was traveling, and when the time for the Maghrib prayer entered, I stopped and entered a mosque at a gas station. I prayed Maghrib in congregation, then I prayed two rak'ahs shortened with the intention of 'Isha' along with a congregation that was praying Maghrib. Is my prayer valid?

Answer:
This is not valid. Because if you pray with a congregation that shortens the prayer, you shorten it with them while you are a traveler. And if you pray with a congregation that completes the prayer, you complete the prayer, even if you are a traveler. This is the sunnah (recommended practice), i.e., what is reported from the Prophet (peace and blessings be upon him), as Ibn 'Abbas said. And you now prayed with an imam who does not shorten; it is not a shortened prayer. The Maghrib prayer is not a shortened prayer. It is obligatory for you to complete your prayer with this imam. Yes.