Sunan Abi Dawud Book 2, Hadith 141
Messenger of Allah, appoint me the leader of the tribe in prayer. He said: You are their leader, but you should follow on who is the weakest of them: and appoint a mu'adhdhin who does not charge for the calling of adhan.
The Messenger of Allah (ﷺ) taught me to say when the adhan for the sunset prayer was called; "O Allah, this is the time when Thy night comes on, Thy day retires, and the voices of Thy summoners are heard, so forgive me."
Bilal made a call to prayer before the break of dawn; the Prophet (ﷺ), therefore, commanded him to return and make a call: Lo! the servant of Allah (i.e. I) had slept (hence this mistake).
The version of Musa has the addition: He returned and made a call: Lo! the servant of Allah had slept.
Abu Dawud said: This tradition has been narrated by al-Darawardi from 'Ubaid Allah on the authority of Ibn 'Umar saying: There was a mu'adhdhin of 'Umar, named Mas'ud. He then narrated the rest of the tradition. This version is more correct than that one.