Is it permissible for non-Muslims to enter mosques?

It is forbidden for disbelievers to enter Al-Masjid Al-Haram, based on the Almighty’s saying: (O you who have believed, indeed the polytheists are unclean, so let them not approach al-Masjid al-Haram after this [current] year of theirs). As for other mosques, it is permissible for them to enter for a legitimate benefit or a need that calls for it, such as hearing what invites them to Islam, or their need for water, following the example of the Prophet, peace and blessings be upon him, who tied Thumamah ibn Uthal and hosted the delegation of Thaqif and the delegation of the Christians of Najran in the mosque before their conversion to Islam, due to the great benefits therein. Therefore, there is no harm in disbelievers entering mosques to witness the Muslims' prayer, unless they have something that would defile the mosque or they are unveiled women.