Deuteronomy 22:22: "If a man be found lying with a woman married to a husband, then they shall both of them die, both the man that lay with the woman, and the woman: so shalt thou put away evil from Israel."
Leviticus 20:10: "And the man that committeth adultery with another man's wife, even he that committeth adultery with his neighbor's wife, the adulterer and the adulteress shall surely be put to death."