Genesis 19:34-38

34And it came to pass on the morrow, that the firstborn said unto the younger, Behold, I lay yesternight with my father: let us make him drink wine this night also; and go thou in, and lie with him, that we may preserve seed of our father.

35And they made their father drink wine that night also: and the younger arose, and lay with him; and he perceived not when she lay down, nor when she arose.

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

37And the firstborn bare a son, and called his name Moab: the same is the father of the Moabites unto this day.

38And the younger, she also bare a son, and called his name Ben–ammi: the same is the father of the children of Ammon unto this day.