It is recommended for the muezzin to call to prayer in one mosque, and it is disliked for him to call to prayer in two mosques and pray in one of them; because if he prays in the first mosque, he is performing a supererogatory act by calling to prayer in the second mosque, and performing supererogatory acts with the call to prayer is not legislated. Additionally, the call to prayer is specific to obligatory prayers, and in the second mosque, he is performing a supererogatory prayer, so it is not appropriate for him to call people to the obligatory prayer when he does not join them in it. See: Al-Bada'i 1: 149-152.