If a traveler finds residents praying the midday prayer and joins them after they have already prayed two units, and he prays the remaining two units with them and concludes the prayer, then learns that they are residents, what should he do?

The questioner : If a person is a traveler and finds people praying the midday prayer, and he is a resident, but he did not know that they were residents, and he only caught up with two units, and he concluded the prayer, then after the prayer, during the interval, he learned that they were...

The Shaykh : ...prayed four units.

The questioner : Yes, so what is the ruling?

The Shaykh : It is obligatory for him to repeat this prayer from which he concluded, because when a traveler joins the imam, his ruling becomes the ruling of the imam.