Ruling on Muslims and Christians exchanging congratulations
Is it permissible for Muslims to exchange greetings with Christians on every occasion?
It is not permissible to greet Christians or other disbelievers on their festivals and religious occasions, for this will be a sort of encouraging them in their falsehood and sharing in their sin. Allah, the Exalted, states, “…but do not help one another in sin and transgression.” [al-Maidah: 2]
However, the prohibition may be lifted if there is an interest, which will most likely be achieved and is required by Purified Shari’ah (Islamic Law).
May Allah grant us success. May peace and blessings be upon our Prophet, his family and Companions