Reference: Fataawa al-Lajnah ad-Daa.imah lil-Buhooth al-‘Ilmiyyah wal-Iftaa., – Volume 3, Page 39, Question 3 of Fatwa No.7360
Question: Is celebrating the Prophet’s birthday halaal or haraam?
Response: Establishing the celebration of the Prophet’s birthday or (the birthday of) other than him is an innovation. And it has been confirmed on the authority of the Prophet ﷺ that he said:
«Whoever introduces anything into this matter of ours (i.e. Islaam) that which is not from it, will have it rejected», [Saheeh al-Bukhaaree/2697 and Saheeh Muslim/1718].
And with Allaah lies all success and may Allaah send prayers and salutations upon our Prophet ﷺ and his family and his companions.