Muhammad is the prophet of Islam. Sources state that, at age 40, he felt himself selected by God to be the Arab prophet of true religion. Throughout his life he continued to have revelations(天の啓示); many are recorded in the Qur'an. Among his fundamental teachings: there is one God; people must in all things submit to Him; nations have been punished for rejecting God's prophets; the world will end with a great judgment. He encouraged frequent prayer and almsgiving(施し), and he forbade usury(高利).