Answered by Shaykh Faraz Rabbani
Question: Assalam alaykum,
My non-Muslim blood sister has invited me to her birthday. Is it allowed for me to go?
Answer: Walaikum assalam,
I pray this finds you in the best of health and spirits.
Birthdays are social—not specifically religious—customs. As such, it is permitted to participate in them, if they are free of fundamentally impermissible activities.
Given that it is your sister, you should also be intended upholding family ties (silat al-rahim), which is one of the great virtues a believer has been commanded to uphold, by Allah and the Messenger (peace and blessings be upon him).
Please see also: Fasting on One’s Birthday and: Innovation (Bid`a) and Celebrating the Prophet’s Birthday (Mawlid) and: Should Converts Break Ties With Non-Muslim Family Members? and: A Reader on Anger Management and Good Character
And Allah is the giver of success and facilitation.