Hassan’s reference is the Islam Islam is an Abrahamic monotheistic religion teaching that Muhammad is a messenger of God. It is the world's second-largest religion behind Christianity, with 1.9 billion followers or 24.9% of the world's population, known as Muslims. Muslims make up a majority of the population in 49 countries. Islam teaches that God is merciful, all-powerful, and unique, and has guided humanity through prophets, revealed scriptures, and natural signs. The primary scriptures of Islam are the Quran, believed to be the verbatim word of God, as well as the teachings and normative examples (called the sunnah, composed of accounts called hadith) of Muhammad. Most Muslims are of one of two denominations: Sunni (85–90%) or Shia (10–15%). Sunni and Shia differences arose from a disagreement over the succession to Muhammad and acquired broader political significance, as well as theological and juridical dimensions. Islam is the fastest-growing major religion in the world.