Musannaf Ibn Abi Shayba 28:271

Abu Usama narrated to us, from Muhammad ibn ‘Amr, from ‘Umar ibn ‘Abd al-‘Aziz, who said: The Sultan is the guardian of the one who fights against the religion, even if he kills a man’s brother or his father. There is no recourse against the one who fights against the religion and strives to cause corruption in the land—meaning, other than the Sultan. And the prescribed punishments (hudud) must not be withheld once they reach the Imam, for establishing them is from the Sunnah.