What are the rulings on combining prayers by delaying them while traveling?

Question:
The questioner says: Honorable Shaykh, we traveled a distance that permits shortening the prayer, and we intended to combine the Maghrib and 'Isha' prayers by delaying them. On the way, we entered the mosque and the imam was praying 'Isha', so we waited until he reached the first rak'ah, then we joined him with the intention of Maghrib and completed the prayer with him. After that, we prayed 'Isha' for two rak'ahs. Is what we did valid or not? And what is obligatory for us if it is not valid?

Answer:
As long as you intended Maghrib and prayed it with the intention of Maghrib, it is valid, if Allah wills, based on the saying of the Messenger (peace and blessings be upon him) However, it is better for you that you pray Maghrib on your own, then join the imam in the 'Isha' prayer, so that there is no confusion or discrepancy in the rak'ahs. They should pray Maghrib first, or if one is alone, he should pray Maghrib first and then join the imam in the remainder of the 'Isha' prayer.