Musannaf Ibn Abi Shaybah 36957 — The words of Isa (peace be upon him)

Salim said: Isa bin Maryam (peace be upon him) said: "Musa forbade you from fornication, and I too forbid you from it. And I forbid you from entertaining thoughts of sin within yourselves. The likeness of this is that of the worm in a beam: even if it does not break it, it hollows it out and weakens it. Or it is like smoke filling a room: even if it does not burn it, it discolours it and makes it foul-smelling."