Abd al-Wahhab argued that all Muslims must individually pledge their allegiance to a single Muslim leader (a Caliph, if there were one). Those who would not conform to this view should be killed, their wives and daughters violated, and their possessions confiscated, he wrote. The list of apostates meriting death included the Shia, Sufis and other Muslim denominations, whom Abd al-Wahhab did not consider to be Muslim at all. There is nothing here that separates Wahhabism from ISIS.

Source: You Can’t Understand ISIS If You Don’t Know the History of Wahhabism in Saudi Arabia | Alastair Crooke