It is noteworthy that Islam encourages tolerance and peaceful co-existence between Muslims and non-Muslims. If non-Muslims enter a mosque to deliver speeches that may lead to a better understanding, then it is welcomed and religiously recommended. Islam is the religion of constructive dialogue in the fullest sense. The history of Muslims is a very good example of this.

In this regard, Sheikh `Atiyyah Saqr, former head of Al-Azhar Fatwa Committee, points out the opinions of Muslim jurists on the issue as follows: Allah Almighty says, (O ye who believe! The idolaters only are unclean. So let them not come near Al-Masjid Al-Haram (at Makkah) after this their year. If ye fear poverty (from the loss of their merchandise) Allah shall preserve you of His bounty if He will. Lo! Allah is Knower, Wise.) (At-Tawbah 9: 28)

And He says, (O ye who believe! Draw not near unto prayer when ye are drunken, till ye know that which ye utter, nor when ye are polluted, save when journeying upon the road, till ye have bathed.) (An-Nisaa’ 4: 43)
Relying on these verses, the majority of Muslim Jurists, including those from the Maliki, Shafi`i and other schools of fiqh (Islamic Jurisprudence), maintain that the polytheists are not allowed to enter the Sacred Mosque in Makkah. However, they state that there is nothing wrong if Christians and Jews enter it. They state that this ruling applies to the Holy Mosque in Makkah as well as its precincts. Abu Hanifah, however, views that even a polytheist can enter the Holy Mosque in Makkah as long as he will not stay or reside there. He interpreted impurity to mean spiritual impurity (shirk).
as for other mosques than the Holy Mosque in Makkah, the Madinan jurists forbade non-Muslims from entering them because non-Muslims are regarded by the Qur’an as impure. Imam Ahmad is reported to have said that they can only enter these mosques with the permission of Muslims. This is supported by the report that the Prophet (peace and blessings be upon him) permitted the people of At-Ta’if to stay in the mosque prior to their embracing Islam. He also received the Christians of Najran in his mosque in Madinah. When the time of their prayer was due, they prayed in the mosque towards the eastern direction. Thereupon the Prophet (peace and blessings be upon him) said (to his Companions), “Leave them (to perform prayer).”

Under the title ‘A Polytheist Entering the Mosque’, Al-Bukhari, in his Sahih mentioned that Thamamah ibn Athal (despite that he was a polytheist) was tied up in the mosque.

In Fath al-Bari, Ibn Hajar mentioned that there are different opinions concerning this issue. The Hanafi jurists gave unconditional permission while the Maliki scholars and al-Mazni are reported to have forbidden it absolutely. The Shafi`i scholars differentiated between the Holy Mosque and other mosques. There is an opinion that the permission is restricted to the People of the Book but this is refuted by the case of Thamamah mentioned above.

Sheikh M. S. Al-Munajjid, a prominent Saudi Islamic lecturer and author, states:

It is forbidden for Muslims to allow any non-Muslim to enter Al-Masjid Al-Haram in Makkah and its sacred precincts, because Allah says: (O ye who believe! The idolaters only are unclean. So let them not come near Al-Masjid Al-Haram (at Makkah) after this their year. If ye fear poverty (from the loss of their merchandise) Allah shall preserve you of His bounty if He will. Lo! Allah is Knower, Wise.) (At-Tawbah 9: 28)
Concerning other mosques, some Muslim jurists maintain that it is permissible for non-Muslims to enter them because there is nothing to indicate the unlawfulness of such act; others say that it is not permissible, by analogy to the case of Al-Masjid Al-Haram.
the correct view is that it is permissible if it serves the interests of Shari`ah or meets a valid need, such as if a non-Muslim needs to enter a mosque to hear something that may encourage him to embrace Islam, or because he needs to drink water, or the like. This is pursuant to the way of the Prophet (peace and blessings be upon him) on this issue; he tied up (his prisoner) Thamaamah ibn Athal Al-Hanafi in the mosque before he became a Muslim, and the delegations of Thaqif and the Christians of Najran stayed in the mosque before they embraced Islam. Actually, many benefits were accrued from this: they were able to hear the speeches and sermons of the Prophet (peace and blessings be upon him) to see people praying and reciting the Qur’an, etc. (Fatawa Al-Lajnah Al-Da’imah – The Standing Committee for Islamic Research and Ifta’)
therefore, if non-Muslims seek permission to enter the mosque in order to see how Muslims perform prayer, there is nothing wrong in that, as long as they have nothing with them that could defile the mosque, and their women are not dressed in a provocative fashion, or any other reason that bars them from entering the mosque. So they can enter and sit behind the Muslims to see how they pray.

Based on the above Fatwas, we can say that non-Muslims, including Christians and Jews, are allowed to enter mosques, but they should abide by the following conditions:

1- non-Muslims are allowed to enter mosques – other than the Sacred Mosque in Makkah – with a prior permission of Muslims.

2- They must have a sound reason for entering the mosque.

3- They should respect the decorum of the mosque and keep in mind that it is a sacred place of worship.

4- Both men and women are not allowed to uncover their `Awarah (parts of the body which should not be exposed in front of others) when entering the mosque.

With regard to the issue of restoration, we can say that Muslims should have the priority in carrying out such work, unless it is necessary to seek the help of non-Muslims. There must be a need to seek their help, especially in issues related to mosques.