During all the Prophets (saws) journeys, Bilal ibn Rabah (raa) was by his side and because of his precedence in embracing Islam, his rich melodious voice and excellent utterance of Quran he was appointed the first Muazzin of Islam. He was the most preferred over all other Muazzins during the Prophets (saws) lifetime and remained in this post at Al-Masjid al-Nabawi (the Mosque of the Prophet) until the Messangers (saws) Death in 10 A.H. (632 A.D.) (Anno Hegirae – year of Hijra).
Bilal (raa) use to announce the Athan (Call to Prayer) especially for the Messanger of Allah (saws) whom he cherished with such deep love by standing next to the door of the Prophets (saws) room shouting "Hasten to the prayer, Hasten to well-being. O Messenger of Allah, prayer.", in response to which the Prophet (saws) would arrive for prayer and Bilal (raa) would announce the Iqama (second call to prayer) before the prayers commenced. It’s because of this personal connection and honour that at the time of the Prophets (saws) passing Bilal (raa) could no longer bear the thought of announcing the call, so he decided to give up announcing the Athan a few days after the demise of Allah’s Apostle (saws) by requesting that Abu Bakr Siddiq (saws) the Caliph release him from his duty of Muazzin and allow him to join the Muhjahideen (strugglers) in Syria.
Bilal Habashi (Bilal the one from Abyssinia) (raa) declined all future requests to announce the Call to Prayer (Athan) except for once, which sadly was the last Call that, he delivered in his lifetime.
To the present day, some scholars are of the opinion that the Athans rhythmical form of recital in the Muslim world is the same as was originated by Bilal (raa). However, it must be clarified that the Messanger of Allah (saws) had not appointed Bilal (raa) as the Muazzin solely because of his masterly rhythm or melody of the rules but it was his exceeding piety, devotion to worship and regular attendance in the Masjid (place of prostration) that the choice of the Prophet (saws) fell on Bilal Habisha (raa) for the performance of this honourable and important duty.