Ruling on non-Muslims entering mosques

There is nothing wrong with non-Muslims entering the mosque
if it is for a legitimate shar’i purpose or for a permissible reason,
such as listening to lessons or drinking water, etc., because the Prophet
(peace and blessings of Allaah
be upon him) let some of the non-Muslim delegations stay in his mosque,
so that they could see the people praying and listen to his recitation
of Qur’aan and his sermons, and so that they could call them to Allaah
from close at hand. And the Prophet
(peace and blessings of Allaah be upon him) tied up Thumaamah ibn Athaal
al-Hanafi in the mosque when he was brought to him as a prisoner of
war, and Allaah guided him and he became a Muslim. And Allaah is the
Source of strength.

From Majmoo’ Fataawa wa Maqaalaat Mutanawwi’ah li Samaahat
al-Shaykh al-‘Allaamah ‘Abd al-‘Azeez ibn ‘Abd-Allaah ibn Baaz (may
Allaah have mercy on him), vol. 8, p.356

 But with regard to groups of tourists entering
mosques just to look around, accompanied by woman who are improperly
dressed and carrying cameras, who enter mosques without respect, this
is a great wrong which should not be allowed. And Allaah is the One
Whose help we seek.