John Gill Commentary Genesis 19:34

"And it came to pass on the morrow, that the first-born said unto the younger, Behold, I lay yesternight with my father: let us make him drink wine this night also; and go thou in, and lie with him, that we may preserve seed of our father." — Genesis 19:34 (ASV)

And it came to pass on the morrow The day following the night, in which the above was transacted.

that the firstborn said to the younger, behold, I lay yesternight with my father informed her, that what they had contrived succeeded according to their wish, and therefore, for her encouragement to go on, proposes to take the same method again.

let us make him drink wine this night also, and go you in [and] lie with him, that we may preserve seed of our father may have children by him, and so our family be kept up, from which it may be hoped the Messiah will spring, (See Gill on Genesis 19:32).