Ibn al-Mājīshün said, “I heard Malik [b. Anas] say, ‘Whoever introduces an innovation (bid’ah) into Islam that he views as good has alleged that Muhammad ﷺ betrayed Messengership. Allaah ﷻ said, “This day, I have perfected your religion for you.. (5:3) [from this we can understand that] whatever was not part of the religion that day is not part of the religion today.’”

→ al-I’tiṣām 1/62 | Imām Abu Isḥāq al-Shātibi [Edition: at-Tawhid] | Translated by: Abu Dawūd [Mustafa b. Saalih] al-Hushayshi

Note [Abu Dawud al-Hushayshi]: to briefly explain the point about the implication of bid’ah being allegations against the Messenger’s conveyance of the Message – it means those who introduce new matters inadvertently disregard the Shari’ah being complete/perfect at the time of the Prophet ﷺ.