Abdullah ibn Zaid had a dream, in which a man visited him and taught him the words of the athan. The companion rushed to the Prophet and told him about the dream, to which the Prophet said, “It is a true dream.” The Prophet then told him to teach the words of the athan to another companion, known as Bilal ibn Rabah, as Bilal had a deep, loud voice. From that moment the rite of the Muslim athan began and until this very moment its sound doesn’t halt around the globe. (Abu Dawoud # 498).