There are different views about your question
- The first view is that it is haram to enter a church
This is the view of the Hanafis and Shaafa’is, but the Shaafa’is limit the prohibition to churches in which there are images, as it says in Tuhfat al-Muhtaaj (2/424), Nihaayat al-Muhtaaj (2/63) and Haashiyata Qalyoobi wa ‘Umayrah ‘ala Sharh al-Muhalla (4/236).
Also,
The Hanafis regard it as haraam in all cases, and they gave as their reason the fact that they are abodes of the devils, as the Hanafi Ibn Nujaym said in al-Bahr al-Raa’iq (7/364) and in Haashiyat Ibn ‘Aabideen (2/43).
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- The second view is that it is makrooh.
This is the view of the Hanbalis, but some of them deduce this to churches in which there are images.
Shaykh al-Islam Ibn Taymiyah (may Allaah have mercy on him) said in al-Fataawa al-Kubra (5/327): The view which most of our companions hold is that it is makrooh to enter churches in which there are images, and this is the correct view concerning which there can be no doubt.
See: al-Furoo’ (5/308), al-Adaab al-Shar’iyyah (3/415) and al-Insaaf (1/496).
They quoted the following as evidence:
It was narrated from Ibn ‘Abbaas (may Allaah be pleased with him) that the Prophet (peace and blessings of Allaah be upon him) saw images in the Ka’bah and he did not enter until he had ordered that they be erased. Narrated by al-Bukhaari (3352).
It was narrated that Ibn ‘Umar (may Allaah be pleased with him) said: Jibreel promised to come to the Prophet (peace and blessings of Allaah be upon him) but he was late and the Prophet (peace and blessings of Allaah be upon him) grew concerned. The Prophet (peace and blessings of Allaah be upon him) went out and saw him, and he told him of his concern and he said to him: “We [angels] do not enter a house in which there is an image or a dog.” Narrated by al-Bukhaari (5960).
It was narrated that Aslam the freed slave of ‘Umar said: When ‘Umar went to Syria, one of the leaders of the Christians made food for him and called him. ‘Umar said: We will not enter your churches because of the images that are in them – meaning the statues. Narrated by ‘Abd al-Razzaaq in al-Musannaf (1/411 and 10/398).
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- The third view is that it is permissible to enter in general.
This is the view of the Hanbalis, as it says in al-Mughni (8/113) and al-Insaaf (1/496).
It is also the view of Ibn Hazm al-Zaahiri as it says in al-Muhalla (1/400).
They quoted the following as evidence:
- What was narrated about the conditions stipulated by ‘Umar to the people of the Book to expand their churches and monasteries so that the Muslims could enter them to spend the night or pass through them.
Al-Mughni (8/113).
- Ibn ‘Aa’idh narrated in Futooh al-Shaam that when ‘Umar came to Syria, the Christians made food for him and called him, and he said: Where is it? They said: In the church, and he refused to go. He said to ‘Ali: Take the people to eat lunch. So ‘Ali took the people and entered the church, and he and the people ate lunch, and ‘Ali looked at the images and said: What would be wrong if the Ameer al-Mu’mineen entered this place?
Al-Mughni (8/113).
However, the above does not make it clear as to whether it is haram or halal.
But it is at least makrooh as the Prophet never entered any building where there were images.
Nowadays, there are a lot of churches which have images. It is makrooh to use them or even enter them as stated above.
When one is organising a Islamic celebration, one should do it at a mosque or building that is made for the purpose of that and not a church.
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Source: Islam Q&A