The Khawārij held it possible that the Messenger himself might act unjustly and lead people astray through his Sunnah. They did not regard obeying and following him as obligatory. They believed him only in what he conveyed of the Quran, not in the Sunnah he prescribed which, they claimed, contradicted the Quran’s apparent meaning. Most proponents of innovation other than the Khawārij follow them in this regard in reality.
They hold that if the Messenger were to say something contrary to their doctrine, they would not follow him, as is related of ʿAmr ibn ʿUbayd concerning the hadith of “the truthful and trustworthy one.” They merely seek to evade the evidence against them, either by rejecting the transmitted report or by reinterpreting its content. Thus, they sometimes impugn the chain of transmission and sometimes the text. In reality, they neither follow nor take as their guide the Sunnah that the Messenger actually brought—or even the Quran as it truly is.
The second distinguishing characteristic of the Khawārij and the people of innovation is that they declare people disbelievers on account of sins and misdeeds. As a consequence, they deem the blood and property of Muslims lawful, regard the abode of Islam as an abode of war, and consider their own abode to be the abode of faith. This is also the position of the majority of the Rāfidah, the majority of the Muʿtazilah, the Jahmiyyah, and a group of extremists affiliated with the scholars of hadith and jurisprudence and their theologians.
This, then, is the root of the innovations identified as such by the explicit Sunnah of Allah’s Messenger, may Allah bless him and grant him peace, and by the consensus of the early generations: treating what is excused as a sin, and treating a sin as disbelief.