Deuteronomy 22:30

Overview - Deuteronomy 22
Of humanity towards brethren.
The sex is to be distinguished by apparel.
The dam is not to be taken with her young ones.
The house must have battlements.
Confusion is to be avoided.
12 Fringes upon the vesture.
13 The punishment of him that slanders his wife.
22 Of adultery;
23 of rape;
28 of fornication;
30 of incest.
Treasury of Scripture Knowledge

Deuteronomy 22:30  (King James Version)
A man shall not take his father's wife, nor discover his father's skirt.

a man shall
This is to be understood as referring to the case of a stepmother. A man in his old age may have married a young woman, and on his dying, his son by another, or a former wife, may desire to espouse her; which is here forbidden.
27:20 Leviticus 18:8 ; 20:11 1 Corinthians 5:1 1 Corinthians 5:13

Ruth 3:9 ; Ezekiel 16:8