Leviticus 20:10
8 You must be sure to obey my statutes. I am the Lord who sanctifies you. 9 “‘If anyone curses his father or mother, he must be put to death. He has cursed his father or mother; his blood guilt is on himself. 10 If a man commits adultery with his neighbor’s wife, both the adulterer and the adulteress must be put to death. 11 If a man goes to bed with his father’s wife, he has exposed his father’s nakedness. Both of them must be put to death; their blood guilt is on themselves. 12 If a man goes to bed with his daughter-in-law, both of them must be put to death. They have committed perversion; their blood guilt is on themselves.
Sirach 23:21
Ben Sira, Ecclesiasticus19 His fear is confined to human eyes and he does not realize that the eyes of the Lord are ten thousand times brighter than the sun; they look upon every aspect of human behavior and see into hidden corners 20 Before the universe was created, it was known to him, and so it is since its completion. 21 This man will be punished in the streets of the city, and where he least suspects it, he will be seized 22 So it is with a woman who leaves her husband and presents him with an heir by another man. 23 For first of all, she has disobeyed the law of the Most High; second, she has committed an offense against her husband; and third, through her fornication she has committed adultery and brought forth children by another man.
Notes and References
"... In the numerical proverb of Sirach 23:16-17 the author sums up the persons or activities that are despicable and cause anger. The first comment on the burning passion is not further specified ("Burning passion is like blazing fire, it will never be quenched until it burns itself out/is consumed"). Nothing indicates whether the person is married, nor what is the object of his passion. In the second element of the proverb, as noted above, behind the Hebrew term is assumed to mean "blood relation" ("The person who commits sexual wrongdoing literally in the body of his flesh, will never cease until the fire burns out"). We find the expression in Leviticus 18:6 and 25:49. The former is part of the incest laws in Leviticus 18:6-18; similar instructions are found also in Leviticus 20:11-12, 14, 17, 19-21. In none of these instances does the LXX use the Greek term of Sirach 23:16. All these instructions deal with a punishable act of a sexual nature and assume that the transgressors are in kinship, whether they live in the same household or not ... it is likely that adultery was not always detected either in pre or in postexilic times, including the time of Ben Sira. It seems, however, that the author anticipates a divine intervention when he points out that even if the man is foolish enough to think that his actions will not be discovered, the Lord, who created everything and therefore knows everything, will see his actions (23:19-20). Therefore the adulterer should be afraid of his sins. Somehow or other the man is apprehended at the end. God's judgment is perhaps not immediate but operates according to its own timetable. 23:21 does not disclose anything about the penalty. The death penalty was probably not in force anymore ..."
Balla, Ibolya Ben Sira on Family, Gender, and Sexuality (pp. 131-134) De Gruyter, 2011