Reference: Fataawa al-Lajnah ad-Daa.imah lil-Buhooth al-‘Ilmiyyah wal-Iftaa. – Volume 3, Page 28, Question 1, Fatwa No. 4683
Question: What is the ruling regarding celebrating the birthday of the Prophet ﷺ, and does the Prophet ﷺ attend [physically or spiritually]?
Response: Respecting the Prophet ﷺ and honouring him is by believing in his mission and acting according to what he came with from Allaah. As for celebrating his birthday then it 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 it is not confirmed that the Prophet ﷺ attends/visits [after his death] anyone from amongst the people, and the principle [of this] is that this does not occur, therefore it is obligatory to remain upon this until [authenticated] evidence suggests otherwise.
And with Allaah lies all success and may Allaah send prayers and salutations upon our Prophet ﷺ and his family and his companions.