Musnad Abu Ya'la al-Mawsili 42:35

Abu Bakr ibn Abi Shaybah narrated to us, 'Abdah ibn Sulayman narrated to us, from Mujalid, from Abu al-Wadak, from Abu Sa'id al-Khudri, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "The group that is most beloved to Allah and the group that is closest to Allah will kill the renegades (al-mariqin)."