Shaykh Ibn Uthaymeen was asked:
“The Christians bought a piece of land to build a church and one of the Muslims donated a large piece of land next to this church to build a masjid. However, some of the Muslims opposed building a masjid near the church and the people hesitated to build the masjid due to that. So what is your view on building a masjid near these church?”
“That which I see is that it is not necessary to build a masjid next to the church because this will lead to fitnah between the Muslims who are confused between the masjid and the church. Or at the very least the Muslims who go to the masjid will say we entered the church and we saw what was in it. So evil will occur. Therefore, I do not see that a masjid be built next to a church and I emphasized that it not be done*.“ End. [Fataawa Thulaathiyyah found here]
This is also the view of some of the Salaf. Tawus rahimahullah said:
لا يَنْبَغِي لَبَيْتِ رَحْمَةٍ أَنْ يَكُونَ عِنْدَ بَيْتِ عَذَابٍ
“It is not correct for a house of mercy to be next to a house of punishment”. End. [Reported by Kitab al-Amwaal of Abu Ubaid no. 286 with a Saheeh chain]
Abu Ubaid rahimahullah said, “I see it to mean churches, synagogues, and places for fire worship. He said, ‘It is not correct for churches to be near masaajid in the Muslim cities’.” End. [Kitab al-Amwaal (1/181)].
Faisal Ibn Abdul Qaadir Ibn Hassan