Moreover you shall not lie carnally with your neighbor's wife, to defile yourself with her.
Leviticus 18:20
Surrounding context
18:19 "Also you shall not approach a woman to uncover her nakedness as long as she is in her customary impurity.
18:20 Moreover you shall not lie carnally with your neighbor's wife, to defile yourself with her.
18:21 And you shall not let any of your descendants pass through the fire to Molech, nor shall you profane the name of your God: I am the LORD.