The second-largest religion in the world is Islam, with over 1.8 billion adherents. Islam is a monotheistic religion that originated in the Arabian Peninsula in the 7th century CE. It is based on the teachings of the Islamic prophet Muhammad and is the world's second-largest religion after Christianity. The core beliefs of Islam are the belief in one God, the prophets of God, the holy books of God, and the Day of Judgment. Muslims believe that Muhammad is the last prophet of God and that the Quran is the final revelation of God.