What is the ruling on congratulating Christians on their holidays, such as saying, "Happy New Year," and visiting their churches on their holidays? And what is the ruling on an Imam who goes to their churches to congratulate them, and what is the ruling on praying behind him?

It is not permissible to congratulate Christians on their holidays because they are among the rituals of disbelief, which are forbidden by consensus. This is akin to congratulating someone for prostrating to the cross. Similarly, it is not permissible to go to churches to participate in their celebrations or to congratulate them, as this involves imitating them and participating in their falsehood. It has been authentically reported that Umar ibn al-Khattab, may Allah be pleased with him, prohibited entering the churches of polytheists on their feast day. As for one who does this, if he does not agree with their disbelieving statements or actions, then merely going does not take him out of Islam, but he has committed a great sin. Prayer behind him is valid, but he should be advised.