Genesis 19:35-39

So they had their father drink wine that night too, and the younger got up and slept with him; and he did not know when she lay down or got up.

And so both of the daughters of Lot conceived by their father.

The firstborn gave birth to a son, and named him Moab; he is the father of the Moabites to this day.

As for the younger, she also gave birth to a son, and named him Ben-ammi; he is the father of the sons of Ammon to this day.