The Christians’ celebrating the ‘Eid of the birth of ‘Eesaa, upon him be peace, is for them. However, it is not permissible for the Muslim to participate in their holidays. They are not to give them gifts at the time of their holidays nor is it befitting to accept their gifts from them at the time of their holidays. Nor is it permissible to sell them anything which will aid them in the celebration of their holidays; all of this is incorrect. This is because it entails being pleased with that which they are upon if the person were to do so. And being pleased with Kufr and the holidays of the disbelievers is prohibited for the Muslims.
Translated By: Raha ibn Donald Batts
Source: http://www.ibnothaimeen.com/all/khotab/article_317.shtml