The Celebration Of The Prophet's Birthday

Textually, the celebration of birthdays whether
personal or for other great Prophet of Allah is
unfounded and baseless in Islam.
Allah says in the Qur'an: Indeed in the Messenger of
Allah (Muhammad SAW) you have a good example
to follow for him who hopes in (the Meeting with)
Allah and the Last Day and remembers Allah much.
Quran (Surah Al-Ahzab, Verse 21)
And it is imperative to follow the guidance of Allah in
all our endeavors.
And I (Allah) created not the jinns and humans
except they should worship Me (Alone).
Qur'an 51 vs 56
Any act of worship not traceable to the Prophet and
his companions is certainly an innovation (bid'a).
The Prophet (peace and blessings of Allaah be upon
him) said he who innovates something in this matter
of ours that is not of it will have it rejected. (Agreed
upon)
The Prophet (peace and blessings of Allaah be upon
him) stated repeatedly that: "Every newly-invented
thing is a bid'ah (innovation), every bid'ah is a going
astray, and every going astray will be in the
Fire." (Reported by al-Nisaa'i in al-Sunan, Salaat
al-'Eedayn, Baab kayfa al-Khutbah). Reports with the
same meaning were narrated via Jaabir (may Allaah
be pleased with him) by Ahmad, via al-'Irbaad ibn
Saariyah by Abu Dawud and via Ibn Mas'ood (may
Allaah be pleased with him) by Ibn Maajah.
The Prophet (peace and blessings of Allaah be upon
him) used to say, when beginning a khutbah
(sermon): " The best of speech is the Book of Allaah
and the best of guidance is the guidance of
Muhammad. The worst of things are those which are
newly-invented, and every innovation is a going
astray" (reported by Muslim, no. 867)
There's a post which summarises that the date of
birth of the Prophet salallahu alayhi wa Salam is
unknown. Read more below.

https://www.nairaland.com/5509901/celebration-prophets-birthday