If a traveler catches up with the imam in the last rak'ah, and does not know whether the imam completed the prayer or shortened it, does he complete it or shorten it?

Question:
He says: Honorable Shaykh, may Allah grant you success. If a person catches up with the imam in the last rak'ah and does not know whether the imam completed the prayer or shortened it, does he complete it or shorten it?

Answer:
He completes it, building on the most cautious position, which is completion. Yes.