Is it permissible to attend the wedding of a Christian friend held in a church, knowing that the accompanying night celebration is unlawful (haram)?

Entering churches is permissible if they are free of reprehensible acts (munkarat). This is the view of Ibn Muflih and Ibn Qudamah, who relied on the opinions of jurists such as Al-Hasan (definition) and Omar ibn Abd al-Aziz. However, if there are reprehensible acts present, such as immodest display, mixing of genders, musical instruments, and singing, then it is not permissible to enter them. Attending a wedding in a church is generally not permissible, as it is unlikely to be free of reprehensible acts. The prohibition becomes even stronger when their falsehoods are recited, due to the Almighty's saying: "And He has already revealed to you in the Book that when you hear the verses of Allah being disbelieved in and scoffed at, then do not sit with them until they enter into another conversation. Indeed, you would then be like them. Indeed Allah will gather the hypocrites and disbelievers in Hell all together." Nevertheless, if the wedding is completely free of reprehensible acts—which is highly unlikely—it is permissible to attend; in fact, it is commendable if it involves inviting to Islam.