All over the Orient dreams have ever been regarded as divine revelations, and the interpretation of them has developed into a distinguished branch of study. Islām, too, has ever attributed a great importance to dreams, especially under Jewish and Stoic influences. Muḥammad's revelation started with visions while he was asleep, and Qur'ān and Ḥadīth contain plenty of allusions to the significance of dreams. Small wonder that the interpretation of dreams ('ilm at-ta'bīr or 'ilm at-ta'wīl) has developed into an important branch of Muslim science, one of the natural sciences together with medicine, physiognomy, alchemy, and astrology, as also with the Greeks. The interpreters of dreams occupied a high rank in society and were reputed to rank with the prophets, whose miraculous qualities they were believed to possess.