From Sahih Bukhari (Hadith 7051):
Abu Sa`id Al-Khudri added that the Prophet (ﷺ) further said:"I will say those people are from me. It will be said, 'You do not know what changes and new things they did after you.' Then I will say, 'Far removed (from mercy), far removed (from mercy), those who changed (the religion) after me
Reference: Bukhari 7051