Ruling on congratulating a Christian teacher or who commits acts of Shirk
First: It is not permissible either to
attend the Christian festivals or congratulate them on such occasions; for this will be a sort of being pleased with what they do, flattering them for their falsehood and helping them in sin and transgression. Allah, the Exalted, says,
Help you one another in Al-Birr and At-Taqwâ (virtue, righteousness and piety); but do not help one another in sin and transgression.
Starting with the greeting to a disbeliever is not permissible; for what has been authentically reported in the Hadith narrated by
Abu Hurayrah (may Allah be pleased with him) that the Messenger of Allah (peace be upon him) said,
Do not greet the Jews and the Christians before they greet you and when you meet anyone of them on the roads force him to go to the narrowest part of it.
Muslim. In the Hadith narrated by
Anas (may Allah be pleased with him), he reported the Messenger of Allah (peace be upon him) as saying,
When the People of the Book offer you salutations, you should say 'The same to you.'
Narrated by the Two Shaykhs (Al-Bukhari and Muslim)Thus they should be answered as indicated in the Hadith by saying, "The same to you." It is all right to start greeting the Kafir (disbeliever) saying "How is it going?" in the morning and the evening, and the like; (Part No. 1; Page No. 449) if necessary. This was acknowledged by a group of scholars including
the Shaykh of Islam Ibn Taymiyyah. Based on what has been mentioned above, it is all right to greet your non-Muslim teachers with any greeting other than that of Islam before they greet you. You can say "How are you?" and the like. Moreover, you can return their greeting if they greet you first. If they learn about the greeting of Islam and greet you with it, you should answer them with what has been mentioned in the previous Hadith saying, "The same to you."May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.