Is it authentic that the adhan was called outside the mosque?

Question:
It is reported in the books of the Sunnah that the mu'adhdhin of the Messenger of Allah (peace and blessings be upon him) used to call the adhan outside the mosque, at the door. Is this an obligatory Sunnah, or a recommended one?

Answer:
No, this is a weak hadith narrated by Abu Dawud with a weak chain of narration. This is because it is transmitted through Ibn Ishaq, who used to summarize his narrations and was a practitioner of concealment (tadlis). Therefore, his hadith is weak when he conceals, and it is not established.
The Sunnah regarding the adhan is that it be called from an elevated place, just as Bilal used to call the adhan from the roof, so that the voice would be clearer. If there is a minaret, as people have built minarets, that is clearer. Now, these loudspeakers have come, and people have been content with them, because the amplified voice reaches those who are far away. For this reason, some people have been content with them instead of a minaret, due to the lack of need for a minaret.