Is it permissible for the muezzin to lead the prayer while he is outside the صف (row) at the back of the mosque, alone?

It is permissible for the one who establishes the prayer (the muqim) to do so while outside the صف (prayer line), and the proof for this is what was narrated about Bilal, may Allah be pleased with him, that he used to establish the prayer while on the minaret, then he would go to the صف. This is also indicated by the Prophet’s, peace be upon him, saying to Bilal: “Do not precede me with ‘Amen’.”

Some jurists have deemed it preferable for the place of iqamah (definition) (establishing the prayer) to be the same as the place of the adhan (definition) (call to prayer). Accordingly, if the mu'adhin establishes the prayer from the place of the adhan through a loudspeaker, it is permissible, because it achieves the purpose of the iqamah, which is to inform the people.

This is also indicated by the apparent meaning of the Prophet's, peace be upon him, saying: “When you hear the iqamah, walk to the prayer.”