Thus were both the daughters of Lot with child by their father.
All Commentaries on Genesis 19:36 Go To Genesis 19
Irenaeus of Lyons
This had happened without Lot’s knowledge and without his having been a slave to pleasure; it was accomplished wholly by divine arrangement, through which the two synagogues born from one and the same father, without carnal pleasure, were evoked. For there was no one else who could give them vital seed and the fruit of children, as it was written. .