Genesis 19:34-38

34On the following day, the firstborn said to the younger, “Behold, I lay last night with my father; let us make him drink wine tonight also; then you go in and lie with him, that we may preserve 1our family through our father.”

35So they made their father drink wine that night also, and the younger arose and lay with him; and he did not know when she lay down or when she arose.

36Thus both the daughters of Lot were with child by their father.

37The firstborn bore a son, and called his name 2Moab; he is the father of the Moabites to this day.

38As for the younger, she also bore a son, and called his name Ben-ammi; he is the father of the 3sons of 4Ammon to this day.