The Messenger of Allah (ﷺ) said to Bilal: Do not call adhan until the dawn appears clearly to you in this way, stretching his hand in latitude.

Abu Dawud said: Shaddad did not see Bilal.
Sunan Abi Dawud Book 2, Hadith 144
← Previous Hadith A mu'adhdhin of ‘Umar, named Masruh, called the Adhan for the morning prayer before the break of dawn; ‘Umar commanded him (to repeat). The narrator reported the tradition in a similar way.

Abu Dawud said: This tradition has been transmitted 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 one.

Sunan Abi Dawud Book 2, Hadith 143 Next Hadith → Ibn Umm Maktum was the mu'adhdhin of the Messenger of Allah (May peace be upon him) and he was blind.

Sunan Abi Dawud Book 2, Hadith 145