Oh. That one is actually cute compared with other examples:
Book of Genesis (chapter 19)
Lot and his two (biological) daughters.
Genesis 19:31-36
31; One day the older daughter said to the younger, “Our father is old, and there is no man around here to give us children—as is the custom all over the earth.
32; Let’s get our father to drink wine and then sleep with him and preserve our family line through our father.”