There was no other mu'adhdhin of the Messenger of Allah (ﷺ). He then narrated the tradition which is incomplete.
Sunan Abi Dawud Book 2, Hadith 701
← Previous Hadith There was no other mu'adhdhin (pronouncer) of the Messenger of Allah (ﷺ) except Bilal.

The narrator then reported the tradition to the same effect.

Sunan Abi Dawud Book 2, Hadith 700 Next Hadith → When the Messenger of Allah (ﷺ) seated himself on the pulpit on a Friday he said, Sit down. Ibn Mas'ud heard that and sat down at the door of mosque, and when the Messenger of Allah (ﷺ) saw him, he said: Come here, 'Abd Allah b. Mas'ud.

Abu Dawud said: This tradition is known as mursal (the successor reports directly from the Prophet, omitting then name of the Companion). The people narrated it from the Prophet (ﷺ) on the authority of 'Ata'. Makhlad is his teacher.

Sunan Abi Dawud Book 2, Hadith 702