The traveler must complete the prayer if he prays behind a resident

Q: I was traveling, and at one of the rest stops, I caught the midday prayer in the rest stop mosque. They were praying the full number of rak'ahs, and when I joined the prayer, the imam was in the first tashahhud. When the imam said the taslim, I said it with him, since I am a traveler. Was my action correct? If not, do I have to repeat the prayer? Please give us a ruling, and may you be rewarded.

A: You must repeat the prayer, because it is obligatory for a traveler who prays behind a resident to pray four rak'ahs; for the Sunnah has been authentically established from the Prophet (peace and blessings be upon him) to this effect. And success is from Allah.