That is not an idea a person of sound mind and nature should entertain. How could someone think of copulating with a woman and her daughter at the same time or one after another? Islam does not allow a man to marry a woman and her daughter.

 

If we were to open the door to it, it would end up mixing the lineages. One of the primary objectives of the Shari`ah is the preservation of offspring.

 

The fact that he committed adultery with the woman should not make a difference. What we stated above is the view of the vast majority of scholars among the companions and successors as well as others.

Almighty Allah knows best.