The Islamic ruling on celebrating Al-Mawlid
Imaam Maalik, may Allah have mercy upon him, said: "What was considered at that time (i.e. the time of the Prophet sallAllahu 'alaihi wa sallam and his companions) as a part of the religion is the religion, otherwise it is not a part of the religion."
It is a historical fact that the Bid'ah of Al-Mawlid was initiated by Al-'Ubaydiyyoon, who were the atheists that ruled the Faatimi state. This Bid'ah was definitely and undoubtedly not practiced by the distinguished first three generations of the Muslim nation, it is a new innovation and it is misguidance. The Prophet sallAllahu 'alaihi wa sallam said: "Every Bid'ah (innovation) is misguidance"(Ahmad, Tirmidhi and others). All new innovation are rejected by Allah because the Prophet sallAllahu 'alaihi wa sallam said: "He who does something which is not according to what we (i.e., the Prophet sallAllahu 'alaihi wa sallam and his companions) are upon then it is rejected" (Muslim). Imaam An-Nawawi, may Allah have mercy upon him, said: "'Rejected' meaning false and not considered by Allah at all." He also said: "This Hadeeth lays down one of the great fundamentals of Islam, which rejects and refutes any new innovation in Islam." He further said: "This Hadeeth must be spread and used as a means to negate all new evils."
Therefore, the Bid'ah of Al-Mawlid is misguidance which is rejected and has no significance to the religion of Islam. source: alminbar.com