Reference: Tanbeehaat Haammah bi-Munaasibati ‘Aam Alfayn – Pages 57-58
Question: So what is the Sharee’ah ruling concerning that which some of the Muslims are doing by taking part in this celebration, even if it is out of courtesy towards the Christians?
Response: It is not permissible to celebrate the occasions of the disbelievers even if it is out of courtesy [towards them]. This is because they are innovated occasions, that which Allaah has not legislated. So there is no basis for them in [any of] the Heavenly Books [from them the Qur.aan, the Injeel (Bible) and the Towraat (Torah)]. Rather they are [from] the innovations of the Christians which they [themselves] have legislated in the religion, that which Allaah has not permitted.
There is no doubt that joining them in this celebration or in any other [celebrations] from their occasions implies an acceptance to these innovations and honouring these innovators! So [based] upon this, it is haraam for the Muslims to honour these occasions and congratulate those who celebrate them or show any [sign] of joy and happiness about them, such that it implies an acceptance for that innovation!! Rather, the Muslims should regard them as [any] other days of the year and should [only] celebrate the occasions legislated by the Sharee’ah with that which has been legislated in terms of salaah and worship, and Allaah [alone] has the Complete knowledge [of all affairs].