Al Allaamah Al Faqeeh Muhammad ibn Saalih Al Uthaymeen (rahimahullah) was asked:
Question: It is said that indeed a bidah is not initiated except that a Sunnah similar to it is abandoned, as one of the salaf stated(1); so what is the abandoned Sunnah as a result of innovating the bidah of mawlid?
Answer: The abandoned Sunnah (in this instance is in relation to) abandoning this bidah because indeed the Sunnah can be by way of [ترك -(abandoning) and by way of فعل (action)]. If the Messenger ( sallal-laahu-alayhi-wasallam ) left something (i.e. an act of worship) despite the fact that there was a means for action, but he did not do it, then leaving it is Sunnah. So here we say: You (people) initiated a bidah and abandoned a sunnah, and Sunnah here is to abandon this bidah.
لقاء الباب المفتوح 210
(1) Know that the people never introduce an innovation until they abandon its like from the Sunnah.
Sharhus Sunnah of Imaam Al Barbahaaree (point 6)