Leviticus 18:20

‘If there is a man who commits adultery with another man’s wife, one who commits adultery with his friend’s wife, the adulterer and the adulteress shall surely be put to death.

and a man lies sexually with her, and it is hidden from the eyes of her husband, and she is undetected; but she has defiled herself, and there is no witness against her, and she has not been caught in the act,

but that we write to them that they abstain from things contaminated by idols and from sexual immorality and from what is strangled and from blood.