Ruling on non-Muslims entering mosques
Question

                Is it permissible to allow Christians, Jews or other non-Muslims to enter mosques to visit them? Some Muslim countries organize such visits for some of the people who visit them.
Praise be to Allah.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.