In Islam, revelation is the basis on which acts of worship are instituted. For this reason, it is forbidden to invent a special ritual and fast on one’s birthday. By doing so, this would be tantamount to initiating a ritual act without having any evidence from authentic sources. At the same time, fasting on one’s birthday can be seen as a way of expressing one’s gratitude to Allah and that is permitted as long as it does not become a ritual act.
Sheikh Ahmad Kutty, Senior Lecturer and Islamic Scholar at the Islamic Institute of Toronto, Canada, states the following: “There is indeed a tradition that indicates that the Prophet used to fast on Mondays. The Prophet (peace and blessings be upon him) used to fast on that day to express his gratitude to Allah the Almighty for giving him life and selecting him as His Prophet. However, it is not allowed to institute a special fast to celebrate birthdays, for that would be tantamount to instituting a ritual act without the sanction of revelation.
At the same time, if a person chooses to give thanks to Allah in this way, without turning it into a ritual, no one can stop him, unless it falls on one of the days when fasting has been prohibited.”