Why don't we celebrate christmas?
لماذا لا نحتفل ؟

الأصل في الأعياد على اختلاف مسمياتها أنها من شعائر الاديان
With regards to these festivals, despite of them having various names, they are from the symbols of religions.

فهي سمة من السمات التي تتميز بها كل ملة وأتباعها عن غيرهم.
It is a defining characteristic of religions and their followers that differentiates them from other religions and its followers.

وقد تواترت النصوص الشرعية بحصر أعياد المسلمين في عيدين كل عام. هما الفطر والأضحى
There are an abundant amount of narrations from the texts of Shariʿah (i.e., the Qur'ān and the Authentic Sunnah) indicating that the annual festivals of the muslims are only two, 'Eīd Al-Fiṭr and 'Eīd Al-Aḍḥā,

وعيد كل أسبوع هو يوم الجمعة.
and the 'Eīd of every week is the day of Jumuʿah (Friday).

قال رسول الله صلى الله عليه وسلم: إن لكل قوم عيدا، وهذا عيدنا.
: "Verily, every nation has an 'Eīd (festival/celebration) and this is ours (i.e., both the ʿEīds)."

وما سوى ذلك من أعياد كالكريسماس ورأس السنة الميلادية وغيرها، فهي لأهل الكتاب.
So other types of annual festivals such as Christmas, New year's and other than that are for the People of the Book (i.e., Jews and Christians).

ولا يجوز للمسلم اعتبارها ولا الاحتفال بها.
Hence, it's not permissible for the Muslim to look forward to these festivals and celebrate them,

ولا التهنئة بها او المشاركة فيها.
Nor is it permissible to extend greetings for them and partake in them.

ويدخل في ذلك: إهداؤهم ما هو من لوازمها،
And what is included in that (prohibition), is gifting them what is necessary for their festivals,

أو بيعهم هذه المستلزمات من أنوار وأشجار. ومأكولات معينة.
Or selling them that which is required like [decor] lights, [Christmas] trees and sweets specific for these festivals.

فإن هذا منهي عنه لسببين:
Verily, this is prohibited for two reasons:

الأول: إن في ذلك تشبها بهم، وإقرارا لهم على كفرهم، وقد حرم الإسلام التشبه بالكافرين فيما هو من خصائصهم.
Firstly: In it is imitation of them, and acceptance of their disbelief, whilst Islam has forbidden imitating the disbelievers in what is exclusive to them (i.e., their religion).

الثاني: إن في هذه الأعياد ابتداعا وإحداثا في دين الله تعالى.
Secondly: In these festivals, there are innovations in the religion of Allāh, the Exalted.

قال ابن القيم رحمه الله: وأما التهنئة بشعائر الكفر المختصة به فحرام بالاتفاق.
Ibn Al-Qayyim (May Allāh have mercy upon him) said: "It's prohibited to congratulate the disbelievers for rituals exclusive to them according to the agreement of the scholars."

كأن يهنئهم بأعيادهم. فيقول: عيد مبارك عليك. أو تهنأ بهذا العيد أو نحوه.
Such as congratulating them on their festivals by saying greetings to you or greetings to you for this festival etc.

فهذا إن سَلم قائله من الكفر، فهو من المحرمات.
Even if the person saying this doesn't fall into Kufr (disbelief) yet it is from what is prohibited.

ولا يعني هذا إساءة المعاملة، ولا الاعتداء.
However, this (i.e., refraining from congratulating them) doesn't display bad mannerism and disrespect.

فإن رفض المشاركة ليس اعتداء، وإنما هو تميز المسلم واستقلاله في معتقداته وشعائره عن غيره.
For indeed, refusing to take part is not disrespect, rather it distinguishes a Muslim in his/her beliefs and symbols from others

ولهذا جاز قبول الهدية منهم.
For this reason, it is allowed to accept gifts from them.

ولا يعد ذلك مشاركة ولا إقرارا للاحتفال.
And it is not considered as partaking or agreeing with their festivals.

بل تؤخذ على سبيل البر وقصد التأليف والدعوة إلى الإسلام.
Rather, it is accepted to show good manners, soften their hearts and call them to Islam

ما لم يكن مما ذبحوه لأجل العيد.
As long as it isn't something they have specifically slaughtered for their festival.

قال شيخ الاسلام ابن تيمية رحمه الله: وأما قبول الهدية منهم يوم عيدهم، فقد قدمنا عن علي بن أبي طالب رضي الله عنه أنه أُتي بهدية النيروز فقبلها.
Shaykhul Islām Ibn Taymiyyah (May Allāh have mercy upon him) said: "As for accepting gifts from them, on their festivals, then we have mentioned regarding ʿAlī bin Abī Ṭālib (May Allāh be pleased with him) that he was given gifts from Nayrūz (a Persian festival for the beginning of their year) and he accepted them."

وعن أبي برزة أنه كان له سكان مجوس فكانوا يهدون له في النيروز والمهرجان. فكان يقول لأهله ما كان من فاكهة، فكلوه. وما كان من غير ذلك، فردوه.
Abū Barzah narrated that some of the Majūs [Magians] who resided with him offered some gifts for during their festivals and rituals. So he would tell his family, "Eat what they give you of the fruits and as for their slaughtered animals return it (to them)."