Genesis 19:34-38

On the following day, the firstborn said to the younger, “Look, I slept last night with my father; let’s make him drink wine tonight too, then you go in and sleep with him, so that we may keep our family alive through our father.”

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.