Deuteronomy 22:22; Leviticus 20:10

22 "If a man is found sleeping with a woman who has a husband, both of them must die -the man who went to bed with the woman and the woman too. In this way you will expel such wickedness from Isra'el.

10 "'If a man commits adultery with another man's wife, that is, with the wife of a fellow countryman, both the adulterer and the adulteress must be put to death.