In the beginning of Islam, there was no prescribed way of informing the people that the time for prayer had began, or to call the Muslims to the mosque for congregational Prayers. When the number of Muslims increased, the holy Prophet(peace be upon him) sought counsel and asked his Companions as to what should be done to call Muslims to the mosque for congregational Prayers. They discussed the question as to how to know the time for the prayer by some familiar means. Some suggested that a fire be lit (at the time of the prayer) and others put forward the proposal to ring the bell

One morning, a companion of the holy Prophet (peace be upon him) approached the holy Prophet (peace be upon him) and related to him a dream which he had had the night before. He had seen someone announcing the Prayer time and calling people to the mosque for the congregational Prayer in a loud voice. 

He then went onto read the prayer which he had heard. The holy Prophet (peace be upon him) ordered another companion (Bilal, peace be upon him) to call the people to prayer with the following words.