Is he who deems it permissible to shake hands with women an apostate, and does the obsessive whisper of showing off affect one's acknowledgment of the impermissibility of shaking hands?

The four jurisprudential schools of thought agree on the prohibition of shaking hands with a young non-mahram woman, but they differ concerning shaking hands with an old woman. Whoever deems permissible something that is unanimously forbidden, and its prohibition is established by definitive proof or is necessarily known, commits an act of disbelief. However, whoever believes something to be forbidden and yet commits it, is sinful but not an unbeliever. One should not pay attention to the whisperings of showing off. The prohibition of shaking hands is indicated by the hadith: "For one of you to be stabbed in the head with an iron needle is better for him than to touch a woman who is not lawful for him."