Genesis 19:36

30 Lot and his two daughters left Zoar and settled in the mountains, for he was afraid to stay in Zoar. He and his two daughters lived in a cave. 31 One day the older daughter said to the younger, "Our father is old, and there is no man around here to lie with us, as is the custom all over the earth. 32 Let's get our father to drink wine and then lie with him and preserve our family line through our father."

33 That night they got their father to drink wine, and the older daughter went in and lay with him. He was not aware of it when she lay down or when she got up.

34 The next day the older daughter said to the younger, "Last night I lay with my father. Let's get him to drink wine again tonight, and you go in and lie with him so we can preserve our family line through our father." 35 So they got their father to drink wine that night also, and the younger daughter went and lay with him. Again he was not aware of it when she lay down or when she got up.

36 So both of Lot's daughters became pregnant by their father. 37 The older daughter had a son, and she named him Moab [g] ; he is the father of the Moabites of today. 38 The younger daughter also had a son, and she named him Ben-Ammi [h] ; he is the father of the Ammonites of today.

Lot's daughters get him drunk and have him impregnate them in order to carry on the family line.