A traveler who combines Maghrib and 'Isha' then finds a congregation praying Maghrib

Question:
I say: Honorable Shaykh, may Allah grant you success. A traveling man wants to combine Maghrib and 'Isha'. After he prays Maghrib, he finds a congregation praying Maghrib, so he wants to pray with them as a congregation with the intention of 'Isha'. It is known that he holds that shortening the prayer is obligatory. Does he pray two rak'ahs, then sit until the imam returns to him to say the closing salam with him? Or does he complete the prayer with them until they finish their Maghrib prayer, then he comes and prays a fourth rak'ah?

Answer:
The better option is that he does not join them, because the form of the prayer differs. Maghrib is a three-rak'ah prayer, and he would differ from the imam. The better option is that he does not join them; he should pray 'Isha' alone or with a group like him. And Allah the Exalted knows best, and may Allah send blessings and peace upon our Prophet Muhammad and upon his family and his Companions.