Musannaf Ibn Abi Shayba 19:301

Abu Bakr narrated to us, he said: Ghundar narrated to us, from Shu'bah, from Hammad, regarding a man who says to another man: "Indeed, upon your back is the prescribed punishment for adultery." He said: If he wishes, he may say: "I only meant that upon your back is a place [for it]." He said: There is no prescribed punishment upon him.