In year 20 of the Muslim era, or the year 641 AD, Muhammad's successor the Caliph Umar decreed that Jews and Christians should be removed from all but the southern and eastern fringes of Arabia—a decree based on the uttering of the Prophet: "Let there not be two religions in Arabia". The two populations in question were the Jews of the Khaybar oasis in the north and the Christians of Najran. Only the Red Sea port of Jeddah was permitted as a "religious quarantine area" and continued to have a small complement of Jewish merchants.