Musannaf Ibn Abi Shayba 19:763

Abu Bakr narrated to us, he said: Muhammad ibn Abi ‘Adi narrated to us, from Ash’ath, from al-Hasan, regarding a man who confesses to a prescribed punishment (hadd) without the authority (sultan) present, then denies it when he is brought before him: He did not see that it should be binding upon him.