Currently, people are celebrating the birthday of our prophet Muhammad (pbuh). Why are we celebrating this event when it's not in the Quran nor in the Sunnah, does that mean it's considered as bid'ah? Bi'dah is to include anything in Islam which was not present at the time of Prophet Muhammad (pbuh). Since this event isn't in the sunnah, there is a hadith that speaks about this matter: Al-‘Irbadd Ibn Sariyah, may Allah be pleased with him, narrated that the Messenger of Allah, prayers and peace of Allah be upon him, said:
“Those of you who live after my death will see many controversies. I urge you to adhere to my Sunnah and the sunnah (way) of my rightly-guided successors (Al-khulafaa’ Ar-Rashidoon) who come after me. Hold onto it as if biting it with your eye teeth. Beware of newly-innovated matters, for every innovation is a going astray.” [Reported by Ahmad, At-Tirmidhi, ibn Majah, Ad-Daarimi, Al-Haakim, Ibn Hibaan, Al-Albani deemed it Saheeh (authentic)].
I don't want opinions on this matter as this is serious, if you are going to post an answer, at least include proof from the sunnah or from the Quran, salaam.