Genesis 19:34 WEB

³²  Come, let's make our father drink wine, and we will lie with him, that we may preserve our father's seed.'

³³  They made their father drink wine that night: and the firstborn went in, and lay with her father. He didn't know when she lay down, nor when she arose.

³⁴  It came to pass on the next day, that the firstborn said to the younger, 'Behold, I lay last night with my father. Let us make him drink wine again, tonight. You go in, and lie with him, that we may preserve our father's seed.'

³⁵  They made their father drink wine that night also. The younger arose, and lay with him. He didn't know when she lay down, nor when she arose.

³⁶  Thus both of Lot's daughters were with child by their father.