What is the ruling on congregants shaking hands with one another after prayer, starting with the Imam, and what should I do if someone extends his hand to shake mine?

The ruling on shaking hands after the Salaam has been previously clarified. If someone extends their hand for a handshake, it should not be refused; rather, one should shake hands while clarifying that this is not from the Sunnah, and that many innovations began with actions whose permissibility was not believed, then they transformed into a Sunnah, where those who opposed it were censured.