Is it Haram for a non-Muslim to enter the mosque? We had a situation where two non-Muslims came to listen to Friday Khutba. When it was time for prayer they got up and prayed with us (they went through the motions). Is that ok? I heard The Prophet, sallallaahu alayhi wa sallam, used to meet with non-Muslims in his Mosque in Medina. Please Advice.

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.

The scholars differed in opinion about the ruling of a non-Muslim entering the mosque. Our view in Islamweb is that it is permissible for a non-Muslim to enter all the mosques if necessary or if there is a benefit like calling him to Islam, with the exception of the Haram Mosque in Makkah.

The evidence for this is that the Prophet sent a military campaign and they captured Thumaamah Ibn Aathaal, who was from the tribe of Hunayfah, so he was tied in the mosque while he was still a disbeliever. [Al-Bukhari and Muslim] So this is an evidence proving the permissibility for a non-Muslim to enter a mosque.

Moreover, Sa'eed Ibn Al-Mussayyib said: "Abu Sufyaan used to enter the mosque of Madeenah while he was still a non-Muslim, and 'Umar Ibn Wahb entered the mosque to kill the Prophet who was inside, and Allaah guided him to Islam." 

Therefore, there is no harm for these two men to enter the mosque in order to listen to the Friday speech. This may lead them to embrace Islam, so it is not appropriate to force them out of the mosque. As regards praying with you while they are still non-Muslims, in principle they should be prevented from it, especially if it is known that they are mocking religion. This has been explained in Fatwa: 88025.

However, if you see that these two men have a real desire to embrace Islam, then we consider that it would be wiser and beneficial to let them perform the prayer at the end of the row while encouraging them to embrace Islam. Besides, you have to show them the benefits of Islam and the reward they would get if they embrace it. You have to explain to them that if they embrace Islam they will have the same rights as Muslims and must fulfill the same obligations like them. 

Allaah knows best.