Does a man touching his wife nullify ablution according to the Shafi'i school?

Touching one's wife's mother does not invalidate ablution, according to the more evident opinion of the Shafi'i school. Al-Nawawi holds that touching a mahram by lineage, suckling, or marriage does not invalidate ablution. The Fiqh Encyclopedia clarifies that touching a mahram does not invalidate ablution, even if with desire, because a mahram is not considered a locus of desire for the individual.