Any child of Muslim parents is considered a Muslim, and Islamic law contains precise and detailed provisions regarding children. Islam is the system of beliefs, rituals, and practices traced back to the Prophet Muhammad (c. 570–632 C.E.), who reportedly started his mission in Arabia in 610 C.E. Islamic law is contained in the Muslim holy book, the Qur'an (or Koran), as revealed to Muhammad. The Qur'an contains 114 suras, or chapters, that were revealed to Muhammad over the course of twenty-three years. There are over one billion Muslims in the world, who inhabit forty predominantly Muslim countries and five continents, traversing a diverse geographical and cultural area. As Islam spread and established itself in these diverse areas, some of the many local cultures and customs became assimilated into Islamic practices. Thus, there may be slight variations on classical Islamic practices from country to country. There are also variations between the two major sects of Islam: the Sunnis and the Shi'is (also spelled Shiite).