Is it obligatory for the resident worshiper to complete the 'Isha prayer if the Imam is a traveler and shortened the prayer?

The Sunnah of the Prophet indicates the permissibility of a resident praying behind a traveler, and that the resident completes his prayer and does not shorten it if his traveling Imam shortens it. The jurists have agreed on this jurisprudence, whereby if the traveling Imam concludes the prayer after two rak'ahs, the resident stands up to complete his prayer to four, based on the saying of the Prophet, peace be upon him: "O people of the town, pray four rak'ahs, for we are people on a journey." The traveling Imam should inform the resident congregants of this before the prayer.