Answer: Arabian peninsula
Explanation: At the time of Muhammad's life, the Arabs, though Abraham's heirs, were mostly polytheists. With the revelation which Muhammad received, his preaching of faith in one God began, and therefore Muhammad is considered to be a prophet of God, in the likeness of Abraham, Moses, Jesus. Muhammad, of course, found resistance among the Arabs to adopt monotheism. There were even conflicts, and one great march by Muhammad and his converts to Islam to the city of Mecca, where there was great resistance to his teaching. Muhammad conquered Mecca, which also marked the conversion of the city's inhabitants to Islam. Not long after that, Muhammad died, and with his death, almost the entire Arabian Peninsula is thought to have been converted to Islam.