At the time of Prophet Muhammad, may the mercy and blessings of God be upon him, there was a group of youth whom whenever they would hear the call to prayer, would imitate and make fun of it.
Muhammad, may the mercy and blessings of God be upon him, heard them and said, “Who did I hear his voice was raised?” To which they pointed to a teen known as “Aba Mahtoora”. The Prophet dismissed the others but Aba Mahtoora to remain. The Prophet intended to develop Aba Mahthoora’s talented voice, for the gift of the Almighty should be used for positive causes to benefit him and all people, instead for unfavorable use.
The Prophet said, “Go ahead and call for prayer”, then taught him the words of the athan, then mentioned, “May God bless you.” As a result, God guided Aba Mahthoora to Islam and he became the “muathan (the one who calls to prayer) of the Prophet in Mecca. This is the story of how Aba Mahthoora started as a disbeliever, who made fun and mockery of the athan, but ended as a truthful believer and the Muathan of the Prophet, may the mercy and blessings of God be upon him. (Musnad Ahmad # 15380).