Genesis 20 · a question people ask
Abraham says Sarah was his half-sister. Wasn't that forbidden?
Genesis records Abraham's words without comment (20:12). The law God gave later through Moses forbids such a marriage: "You shall not uncover the nakedness of your sister, the daughter of your father, or the daughter of your mother" (Leviticus 18:9; also 20:17). Abraham lived long before that law was given, and Genesis doesn't say how God regarded such a marriage before then.
The verses
“Besides, she is indeed my sister, the daughter of my father, but not the daughter of my mother; and she became my wife.”
““‘You shall not uncover the nakedness of your sister, the daughter of your father, or the daughter of your mother, whether born at home or born abroad.”
““‘If a man takes his sister—his father’s daughter, or his mother’s daughter—and sees her nakedness, and she sees his nakedness, it is a shameful thing. They shall be cut off in the sight of the children of their people. He has uncovered his sister’s nakedness. He shall bear his iniquity.”