If a man lusts after his mother-in-law, does his marriage to her daughter become void?

We have not come across anyone who stated that the mere occurrence of desire in a man's heart for his wife's mother invalidates his marriage to her daughter. As for deriving pleasure from the wife's mother, the Hanafi school holds that it renders the wife unlawful if it is done with intent to derive pleasure, such as kissing or touching her with desire. The Malikis wavered on this issue. What is reported from Ahmad is that only intercourse renders her unlawful. As for the Shafi'is, they do not consider the wife unlawful due to any of that, even if the husband were to commit intercourse with his wife's mother. This is the more preponderant opinion, based on the saying of Ibn Abbas: "If he commits zina with her, his wife does not become unlawful for him."