Genesis 19:34-38

34It happened on the next day that the firstborn said to the younger, “Indeed I lay with my father last night; let us make him drink wine tonight also, and you go in and lie with him, that we may preserve the lineage of our father.”

35Then 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 Moab; he is the father of the Moabites to this day.

38And the younger, she also bore a son and called his name Ben-Ammi; he is the father of the people of Ammon to this day.