Where should one pray: in the small, informal mosque—and is it considered a mosque?—or in the nearby جامع (Jāmi‘) mosque? And how can one determine the reach of the Jāmi‘ mosque’s adhan (call to prayer)?

If the owner of the land gives permission for prayers to be performed in it for a specific period, without intending to make it a mosque, then it is not a mosque, and praying in it is permissible. However, if he dedicates it as a waqf and makes it a mosque, then if the construction of the second mosque is out of necessity, it becomes a mosque simply by virtue of being made a wa waqf. Prayers are permissible in it, even if the dedication as a waqf is not explicitly stated, but rather indicated by actions that are customarily understood as such. However, if it is built without necessity, do not pray in it.