Genesis 19:33-38

So they made their father drink wine that night. And the firstborn went in and lay with her father. He did not know when she lay down or when she arose. The next 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 offspring from our father.” So 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. Thus both the daughters of Lot became pregnant by their father. The firstborn bore a son and called his name Moab. He is the father of the Moabites to this day. The younger also bore a son and called his name Ben-ammi. He is the father of the Ammonites to this day.