Eid-e-Milad-e-Habeebullah Swallallahu Alaihi wa Sallam is not a new practice. Be known, The final Rasul Habeebullah Hudur Pak Swallallahu Alaihi wa Sallam Himself had discussed His Biladat (Birth) Shareef.
It is described in sacred Hadith Shareef-
Meaning: It is described Hadrat Abdullah Ibn Umar Rawdiallahu Ta’la Anhuma. The Habeeb of Allah Pak, Hudur Pak Swallallahu Alaihi wa Sallam declares, “When Allah Pak creates the species, He creates Bani Adam as the best of all. He likes Arab best among Bani Adam. And He likes Muddark among Arab, Quraish among Muddark, Bani Hashim among Qurayeesh and me among Bani Hasheem best of all. Certainly, I am the best of the best.” Subhanallah! Ref: Bayhaki Shareef, Tabrani Shareef, Khasyeesul Kubra, Abu Nayeem.
Meaning: Hadrat Abbas Rawdiallahu Ta’la Anhu describes, “Once I presented to Rasulullah Swallallahu Alaihi wa Sallam. In the meantime, some people commented wrong on our clan. Probably, this news is informed by Habeebullah Hudur Pak Swallallahu Alaihi wa Sallam. There were many people on that time.” Standing on Mimbar (Dias) He asked, “Who am I?” All the people replied, “You are the Rasul of Magnificent Allah Pak.” Then He declares, “I am Hadrat Muhmmad Swallallahu Alaihi wa Sallam who is the son of Hadrat Abdullah Alaihis Salam, the grandson of Hadrat Abdul Muttalib Alaihis Salam. Magnificent Allah Pak creates me in the best Quraish clan among the best species of the whole universe, in the best Hashemi tribe among the Quraish clan and in the best house among the world of Allah.” Ref: Tirmidhi Shareef-3532, Musnade Ahmad Shareef-1791, Mishqat Shareef, Mirkat Shareef-57/11, Ahmad, Kanjul Ummal -21947
Meaning: It is described from Hadrat Abdullah Ibn Abbas Rawdiallahu Ta’la Anhu. Noor-e-Mujassam Habeebullah Swallallahu Alaihi wa Sallam declares, “Certainly, Allah Pak divided the whole creations in two division and keeps me in the best part. Subhanallah! Then keeps me in the best clan among the clans divided by Allah. Subhanallah! Then keeps me in the best family among the family divided by Him. Subhanallah! That’s why Magnificent Allah Pak declares, “Hey, the most honored Ahlu Bayit (Descendants) Shareef Alaihis Salam! Certainly, Allah Pak wants to keep you sacred removing all impurity from you.” “It means, Allah creates you doing sacred.” Subhanallah! And I and my most honored Hadrat Ahlu Bait Shareef Alaihimus Salam means we are pure from all sins and dislikings.” Subhanallah! Ref: Dalayilun Nubuwah leel Bayhaki, Ash Shifa-1/325, Sirate Halbiyah-1/42, Al Marifatu wat Tarikh-1/498, Khasyisul Kubra-1/66. Subulul Huda war Rashad-1/235
So, who will go against Sahih Hadith Shareef, say Bidwat (new thing) whether he is believer or not…!