Is it okay to have a Christian teacher or friend? I look forward to your answer.

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.

The term friendship means love and affection. Therefore, it is not permissible for a Muslim to befriend a non-Muslim, whether he is a Jew, a Christian or of any other religion. Also, it is not permissible to socialize with them or befriend them because this leads to loving them and being  loyal to them. Allaah Says (what means): {You (O Muhammad) will not find any people who believe in Allaah and the Last Day, making friendship with those who oppose Allaah and His Messenger (Muhammad), even though they were their fathers, or their sons, or their brothers, or their kindred (people). For such He has written Faith in their hearts, and strengthened them with Rûh (proofs, light and true guidance) from Himself. And We will admit them to Gardens (Paradise) under which rivers flow, to dwell therein (forever). Allaah is pleased with them, and they with Him. They are the Party of Allaah. Verily, it is the Party of Allaah that will be the successful.} [Quran 58:22]

The matter is even more forbidden and more serious if the friendship is between a Muslim woman and a non-Muslim man, or between a Muslim man and a non-Muslim woman, because this involves evil that leads to committing Zina (fornication and/or adultery).

Therefore, a Muslim should be very careful and cautious about this, because being friendly to non-Muslims is very serious. Allaah Says (what means): {O you who believe! Take not as intimate those outside your religion (pagans, Jews, Christians, and hypocrites) since they will not fail to do their best to corrupt you. They desire to harm you severely. Hatred has already appeared from their mouths, but what their breasts conceal is far worse. Indeed We have made plain to you the signs if you understand.} [Quran 3:118] Besides, the Prophet, sallallaahu ‘alayhi wa sallam, said: "A person is upon the religion of his friend, so you have to choose whom you befriend." [Abu Daawood, At-Tirmithi and others]

However, dealing with them in fields like buying  and selling, studying and so on, without taking them as friends, is permissible, but the following requirements must be met:

1-    Believing that any religion other than Islam is null and that whoever practises a religion other than Islam is a disbeliever, as Allaah Says (what means): {Truly, the religion with Allaah is Islam.} [Quran 3:19] Allaah also Says (what means): {And whoever seeks a religion other than Islam, it will never be accepted of him, and in the Hereafter he will be one of the losers.} [Quran 3:85]

2-    Not being loyal to or loving them: Allaah Says (what means): {O you who believe! Take not My enemies and your enemies (i.e. disbelievers and polytheists, etc.) as friends, showing affection towards them, while they have disbelieved in what has come to you of the truth (i.e. Islamic Monotheism, this Quran, and Muhammad)} [Quran 60:1].

3-    However, this does not mean that it is permissible for a Muslim to  be unjust to them if they are not belligerent; rather, a Muslim is obliged to deal justly with them and it is forbidden for him to treat the unjustly. Allaah Says (what means):

Allaah Knows best.