Is it permissible for travelers to shorten the prayer in congregation with an imam and followers?

Travelers pray in congregation, shortening the four-rak'ah prayers. It is permissible for a traveling Imam to lead residents in prayer; he leads them for two rak'ahs, and then the residents complete their prayer. The Prophet (peace be upon him) stayed in Mecca for eighteen nights, leading people in prayer with two rak'ahs, and he would say: "O people of Mecca, stand and pray two more rak'ahs, for we are a traveling folk." Congregational prayer for travelers is legislated and recommended, and some scholars have gone to the extent of saying it is obligatory.