Why do we celebrate Eid Milad-un-Nabi(P.B.U.H)if to celebrate a birthday is wrong?

Why do we celebrate Eid Milad-un-Nabi(P.B.U.H)if to celebrate a birthday is wrong

That should not be celebrated either,it is considered a bid'ah (an innovation).

In tafseer duraiy mansoor written by Hazrat Imam Jallal Udiyeen Salluwti narrates 'who ever does my zikr(Allah)But does not do the Zikr of prophet Muhammad S.A he is not destined for Jannat'