Shaykh Muḥammad ibn Ṣāliḥ al-ʿUthaymīn (d. 1421 AH/2001 CE) ؒ said:
As for extending greetings to non-Muslims on their festivals, then this, without doubt, is forbidden and could, in some instances, be disbelief, as wishing them well on the occasions of their festivals shows one’s approval of them, and showing approval of acts of disbelief is itself an act of disbelief.
This includes wishing them well on what is known as Christmas, or Easter and the likes. This is not permissible whatever the case may be. Even if they wish us well on our festivals we do not wish them well on their festivals.
And the difference is that when they wish us well on our festivals, they wish us well for something that is right. Whilst if we were to wish them well on their festivals, we would be wishing them well for something that is wrong. This is the difference.
We therefore do not say we are returning the gesture. If they extend greetings to us on our festivals we should not extend them greetings on their festivals, due to the difference mentioned earlier.
References
Shaykh Muḥammad ibn Ṣāliḥ al-ʿUthaymīn, statement concerning greetings on non-Muslim festivals. The original article did not supply source details.
