What is the ruling on someone who prayed behind a resident imam while he was a traveler, and the imam completed the prayer and saluted at the second rak'ah?

The congregant must follow the imam even if the latter makes a mistake, because the Messenger of Allah, peace and blessings be upon him, said: "Indeed, the Imam is appointed to be followed." If a traveler prays behind a resident imam, he must pray a full prayer and not shorten it; otherwise, his prayer is invalid and he must repeat it. Umar, may Allah be pleased with him, said to someone who did not follow his imam: "You neither prayed alone nor followed your imam." Ibn Taymiyyah said: "The prayer of the congregant is determined by the prayer of the imam."