The ruling on a traveler who prays behind a resident imam

The questioner:
So, what is the ruling on prayer, O Shaykh, regarding shortening and combining while traveling? If I come upon a person while I am traveling, and he is from the people of the town where I am praying, and I find that he is completing, for example, the 'Asr prayer, and I did not realize he was from the people of the town until the second rak'ah, so I caught up with him and I had missed one rak'ah of the 'Asr prayer. He prayed three rak'ahs, and I was shortening, so I prayed and I was forced to complete the third with him and I said the taslim with him. Is this correct or incorrect?

The Shaykh:
My brother, if you pray behind an imam who completes the prayer, you are required to complete it, because your ruling is the same as the imam's. You do not shorten the prayer behind one who completes it. Yes.

The questioner:
In this ruling, since he prayed three rak'ahs, do I complete the fourth or do I say the taslim?

The Shaykh:
Yes, you complete the fourth.

The questioner:
Yes, may Allah reward you with good. Fine.

The Shaykh:
Application.