The ruling on a traveler shortening the prayer if he catches up with one rak'ah of the residents' congregation

Question:
The questioner says: If I am traveling and the time for the prayer has entered, and I enter the mosque where there is a congregation finishing the prayer, and I only catch up with them for one rak'ah, do I complete the prayer or shorten it?

Answer:
It is not permissible for you to shorten the prayer; because this imam is completing the prayer, and he is not traveling, so you are required to complete the prayer following the imam, even if you did not arrive until before the taslim. If you entered with him before the taslim, you are required to complete the prayer; because your ruling is the ruling of this imam.