Similarly, Christians celebrate religious events based on their explanation of their religion. One of these events is Christmas.
The theory associated with Christmas is that 25th December is the birthday of Jesus Christ according to christians. An important fact, however, is that not every christian believes in this. It is actually, date of birth of the pagan king Constantinople who changed the very foundations of Christianity.
There is also a figure associated with Christmas called Santa clause. While all over the world, Christians and non Christians associate him with Christianity, the reality is that this figure is no where mentioned in any version of bible.
The Islam's take on Christmas and stories associated with it is that this is all false and absurd. First of all, no one knows the exact date of birth of Jesus Christ PBUH. Secondly, it is christian belief that Jesus PBUH is son of GOD ( Na'udubillah) which is shirk and biggest of all the lies. So, this is one of the main reason why Muslims must not wish Christmas. ALLAH swt has spoken in very strict words about those who think ALLAH swt has a son. The noble verse of glorious Quran given below says that;
AL-Quran-9:30
The Jews say, "Ezra (Ozair) is God's son"; and the Christians say, "The Messiah is God's son." Such the sayings in their mouths! They resemble the saying of the Infidels of old! God do battle with them! How are they misguided!
Secondly, Santa Claus, the figure associated with Christmas is not real still he is presented as a godly being watching over world and distributing heavenly gifts. This again, is absurd because no such being is real according to islam. Islam believes in plain logic. Even for some incidents where our logic seems to fail, there is a proper explanation to it in islam. So, based on islam, no false story like Christmas is true or should be celebrated.
It is collective decision of all the well known and famous religious scholars of old an new age that wishing any non-islamic festival which is based on non-islamic tradition is haram i.e. not permissible.
Sheikh Ibn-e Uthaymeen (may Allah have mercy on him) said:
“it is forbidden for the Muslims to imitate the kuffaar by holding parties on these occasions, or exchanging gifts, or distributing sweets or other foods, or taking time off work and so on, because the Prophet (blessings and peace of Allah be upon him) said: “Whoever imitates a people is one of them.”
Shaykh al-Islam Ibn Taymiyah said:
Imitating them on some of their festivals implies that one is happy with the falsehood they are following, and that could make them (the non-Muslims) take this opportunity to mislead those who are weak in faith. End quote.
[End quote from Fataawa Ibn ‘Uthaymeen, 3/44]
Based on these fatawa, is is clear that wishing Christmas is haram and a sin.