Musnad Ahmad 26:500

Abu Mu'awiyah and Waki' narrated to us, they said: Al-A'mash narrated to us, from Muslim ibn Sabih, from Masruq, from Abdullah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Indeed, among the people who will receive the severest punishment on the Day of Resurrection are the image-makers." And Waki' said: "The severest of people."