No doubt that the stance of the Kharijites from the Hadith was based on their stance from its narrators i.e., the Companions of the Prophet (peace be upon him).
The books of history and sects are of agreement that the Kharijites, no matter the difference of their sects, said that all the Companions were trustworthy before the sedition then they called the following Companions disbelievers: Ali, `Uthman, the people who fought in the Battle of Al Jamal, and all the Companions after arbitration, including the two judges, those who satisfied with the arbitration and those who said about the judges they were right or even one of them was right. They called them unbelievers because they disobeyed the command of Allah. (1)
As a result to their apostasy, they rejected the Hadiths of the Companions after the sedition, refused to accept their narrations, and refused to accept the narrations of the Muslim jurists who verified and judged the narrations of the Companions and used analogy and gave their own views based on the Fatwas of the Companions, therefore they called them disbelievers too. (2)
Thereby, they fell into terrible errors that contradicted the sound reason among which their aversion from the Sunnah and narrations.
Dr. As-Siba`y said: "It was a serious sedition that the trustworthiness of the Companions, who participated in the dispute between Ali or Mu`awiyah, was doubted, their Hadiths were rejected, and called them disbelievers or dissolute. By that view, they are not less dangerous than the Shi`ite because their views are corrupted. If the standard to accept a narration is the truthfulness and integrity of the Companions in all they conveyed to us, and lie cannot be attributed to them because of their nature, religion, and rearing, what is the connection between their selves and their political views and errors? And why to describe them with qualities that are not proper to describe common people; how about the Companions of the Messenger of Allah (peace be upon him) who served Islam with all they could. Except if the Companions had not conveyed the message to us, we would have remained in darkness and we would not have known anything about guidance." (3)
(1) See: Al Farq Bayna Al Firaq p. 74 As-Sunnah Wamkantuha Fi At-Tashri` Al Islamy p. 149. The stance of the Kharijites is contrary to the stance of the people of the Sunnah who certified all the Companions and called them trustworthy whether they participated in the dispute or not.
(2) See: Al Farq bayna Al Firaq p. 322.
(3) As-Sunnah Wamkantuha Fi At-Tashri` Al Islamy p. 133 with paraphrasing.