What is the ruling on the Dhuhr prayer for a traveler who set out after its time began, traveling a distance of ten kilometers? Should he pray it in full or shorten it?

The majority opinion is that a traveler performs the traveler's prayer (qasr) once they have left the city, because the Prophet, peace and blessings be upon him, did not shorten prayers until he had departed Medina. Thus, he prays two rak'ahs. The determining factor is the time of the action. So, if the call to prayer (adhan) is made and the traveler has left and passed the populated area of the city, it becomes permissible for him to shorten the four-rak'ah prayers, because at the time of the action, he is a traveler.