What should a traveler intend if he enters prayer with a congregation he does not know whether they are residents or not, and he has not yet prayed Maghrib?

It is not permissible to begin prayer without specifying it. If the worshiper does not specify his prayer, his prayer is invalid under any circumstances. Maghrib prayer must precede 'Isha prayer due to the obligation of sequential order between the two present prayers. It is permissible to follow the Imam even with a difference in intention, such as one praying Maghrib behind an Imam who is praying 'Isha. If the Imam is a traveler and shortens the prayer, the worshiper praying Maghrib completes his prayer after the Imam's salutation. If the Imam is not a traveler, the worshiper praying Maghrib sits for the tashahhud in the third rak'ah, intends to separate from the Imam, then recites the tashahhud and makes the salutation.