And yet indeed [she is] my sister
In the same sense as Lot was his brother; for she was sister to Lot, and both were the children of Haran, the brother of Abraham: she [is] the daughter of my father, but not the daughter of my mother;
she was the daughter of his father, being his granddaughter, grandchildren are sometimes called children, but not the daughter or granddaughter of Abraham's mother; Terah having had two wives, by the one he had Haran, the father of Sarah, and by the other Abraham. According to the Arabic writers F6, Abraham and Sarah were the immediate children of Terah, but by two mothers:
``the mother of Abraham (they say) died, whose name was Juna, and Terah married another wife, whose name was Lahazib, some say Tahuitha, who bore him Sarah, afterwards married to Abraham; hence Abraham said, she is my sister on my father's side, but not on my mother's side:''and she became my wife;
as in those times it was judged lawful, and so it has been accounted lawful in many nations to marry sisters on the father's side, when those on the mother's were prohibited F7.
F6 Elmacinus, p. 51. Patricides, p. 17. apud Hottinger. Smegma Oriental. p. 281.
F7 Vid. Philo. de Special. Leg. p. 779. Clement. Alex. Stromat. l. 2. p. 421.