Genesis 19:33-38

So they made their father drink wine that night, and the firstborn went in and lay with her father; and he did not know when she lay down or when she arose. On 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 our family through 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 were with child by their father. The firstborn bore a son, and called his name Moab; he is the father of the Moabites to this day. As for the younger, she also bore a son, and called his name Ben-ammi; he is the father of the sons of Ammon to this day.