Answered by Shaykh Faraz Rabbani
Question :What is the ruling for commemorating one’s birthday by fasting on it (like the Prophet Allah bless him and give him peace is reported to have done)?
Answer: It is mentioned in several works that simply commemorating one’s day of birth is not blameworthy, if it is done in a way that is related to remembering and giving thanks for the blessings of Allah Most High. However, the closer such celebration comes to the ways of the unbelievers, the more disliked it would be, especially if one seeks to imitate or be like them, for the Prophet (Allah bless him and give him peace) said, “Whoever loves a people is of them.”
Wassalam,
Faraz Rabbani