Much debate regarding the subject of the Mawlid has taken place and continues to take place. The confusion regarding this subject returns back to the lack of clarity about what precisely is the nature of the innovation (bidʿah) that the legislation of Islam, the Shariʿah, has prohibited and warned against.
As for birthday celebrations, they have their origins and practice with the greatest disbelievers, polytheists and tyrants upon the Earth such as Pharoah and Ptolemy and are connected to magic, astrology and the casting of horoscopes. They were unknown to the Prophets of Bani Israʾil and unknown in the legislations which Allah revealed to them. Likewise, the early Christian Church, for the first three hundred years at least, never celebrated birthdays until the era of Constantine the Pagan Roman Emperor in the fourth century CE who merged what was already, by that time, a gross distortion of the clear message of Jesus (alayhis salaam) with Paganism, its symbols and customs.
It was the Ismaʾili Baṭini Shiʿite hypocrites and disbelievers who entered this practice among the Muslims three centuries after the era of the Companions of the Prophet (sallallaahu alayhi wasallam). This work provides a thorough historical and legislative treatment of this subject and addresses the foundational and subsidiary arguments used to justify this innovated practice.
Author - Imam Ibn Qayyim Al-Jauziyah