They know Sahaba never celebrated Mawlid un Nabi Peace be upon him still they abuse those who do not celebrated.
a) Ghulam Rasool Saeedi brailwi Shaykh ul Hadith Jamiyah Naeemiya, who wrote the best Sharh of Sahih Muslim in urdu according to them states:
“It is true that the righteous predecessors Sahaba and Tabiyeen never arranged mawlid gatherings but sahaba and tabiyeen did not stop (others) to do this…. One of the reason due to which sahaba and tabiyeen did not arrange the mawlid gatherings was that they were busy IN MORE IMPORTANT works night and day. Like Jihad in the way of Allah, Making the Kuffar Muslim…[Sharh Sahih Muslim vol 3 page 179 ]
b) Tahir ul Qadri said
Chapter 7 “Why the Muslims of Quroone Aula (Sahaba,Tabiyeen and itteba tabiyeen) didn’t celebrate Mawlid?”
Qadri mentioned reasons:
Translation: The death of Prophet peace be upon him was very hurting for his Companions May Allah be please with them.
Then Qadri wrote in last two lines of this heading
“By remembering the death of Beloved peace be upon him, companions could not celebrate with shocked hearts (of people). So they did not celebrate mawlid neither they were dis hearted in the grief of death”. [Meelad un Nabi, Chapter no: 7, Page no:454 Minhaj ul Quran Publications]