How can the birth of the Messenger, may Allah’s prayers and peace be upon him, and the birth of our Master Jesus, may peace be upon him, be celebrated without violating Islamic law?

It is not prescribed to celebrate the birth of the Prophet, peace and blessings be upon him, nor that of any other prophets, because neither the Prophet, peace and blessings be upon him, nor his companions, nor the Tabi'un did so. Had it been good, they would have preceded us to it. Their ترك (abandonment) of it indicates its innovated nature. This does not contradict the recommendation to fast on Mondays, as it is the day of his birth, the day the revelation descended upon him, and the day deeds are presented.