If they greet us on the occasion of their festivals, we should not respond, because these are not our festivals and because they are not festivals that are acceptable to Allaah. These festivals are innovations in their religions, and even those which may have been prescribed formerly have been abrogated by the religion of Islaam, with which Allaah sent Muhammad (peace and blessings of Allaah be upon him) to the whole of mankind. Allaah says (interpretation of the meaning):
"Whoever seeks a religion other than Islaam, it will never be accepted of him, and in the Hereafter he will be one of the losers." [Aal ‘Imraan 3:85]
It is haraam for a Muslim to accept invitations on such occasions, because this is worse than congratulating them as it implies taking part in their celebrations.
Similarly, Muslims are forbidden to imitate the kuffaar by having parties on such occasions, or exchanging gifts, or giving out sweets or food, or taking time off work, etc., because the Prophet (peace and blessings of Allaah be upon him) said: "Whoever imitates a people is one of them."
Shaykh al-Islaam Ibn Taymiyah said in his book Iqtidaa’ al-siraat al-mustaqeem mukhaalifat ashaab al-jaheem: "Imitating them in some of their festivals implies that one is pleased with their false beliefs and practices, and gives them the hope that they may have the opportunity to humiliate and mislead the weak."
Whoever does anything of this sort is a sinner, whether he does it out of politeness or to be friendly, or because he is too shy to refuse, or for whatever other reason, because this is hypocrisy in Islaam, and because it makes the kuffaar feel proud of their religion.
Allaah is the One Whom we ask to make the Muslims feel proud of their religion, to help them adhere steadfastly to it, and to make them victorious over their enemies, for He is the Strong and Omnipotent.
Majmoo’ah Fataawa wa Rasaa’il al-Shaykh Ibn ‘Uthaymeen,( 3/369)
it is not permissible to give a kaafir a gift on the day of one of his festivals, because that is regarded as approving of or participating in the celebration of the false festival.
If the gift is something that will help in celebrating the festival, such as food, candles, and the like, then it is even more haraam, and some of the scholars are of the view that this is kufr.
With regard to accepting a gift from a kaafir on the day of his festival, there is nothing wrong with that, and that is not regarded as participating in it or approving of it, rather it should be accepted as an act of kindness, with the aim of softening his heart and calling him to Islam. Allaah has permitted kindness and fair treatment towards the kaafir who is not fighting the Muslims, as He says (interpretation of the meaning):
“Allaah does not forbid you to deal justly and kindly with those who fought not against you on account of religion nor drove you out of your homes. Verily, Allaah loves those who deal with equity” [al-Mumtahanah 60:8]
But kindness and fair treatment does not mean friendship and love, because it is not permitted to take a kaafir as a friend or love him. Allaah says (interpretation of the meaning):
“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 Rooh (proofs, light and true guidance) from Himself. And He 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” [al-Mujaadilah 58:22]
“O you who believe! Take not My enemies and your enemies (i.e. disbelievers and polytheists) as friends, showing affection towards them, while they have disbelieved in what has come to you of the truth” [al-Mumtahanah 60:1]
“O you who believe! Take not as (your) Bitaanah (advisors, consultants, protectors, helpers, friends) 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 Ayaat (proofs, evidences, verses) if you understand” [Aal ‘Imraan 3:118]
“And incline not toward those who do wrong, lest the Fire should touch you, and you have no protectors other than Allaah, nor you would then be helped” [Hood 12:113]
“O you who believe! Take not the Jews and the Christians as Awliyaa’ (friends, protectors, helpers), they are but Awliyaa’ of each other. And if any amongst you takes them (as Awliyaa’), then surely, he is one of them. Verily, Allaah guides not those people who are the Zaalimoon (polytheists and wrongdoers and unjust)” [al-Maa’idah 5:51]
The Muslim should be proud of his religion and apply its rulings, and he should not give them up out of shyness or to impress anyone, for Allaah is more deserving of us feeling shy before Him.