The Khawarij are probably the first sect among Muslims. During the caliphate of Ali (may Allah be pleased with him), this group of people broke away from the group of Muslims and accused them, and Caliph Ali (may Allah be pleased with him), of disbelief. They killed innocent Muslims, fought the Muslim army and spread corruption. Abdullah Bin Abbas sought permission from the Caliph and went to convince the group how they had erroneous understanding of Islam. The following is the debate in Ibn Abbas's own words: “I have come to you from the companions of the Messenger of Allah (peace be upon him), from the Muhajiroun and the Ansar, so that I may inform you of what they say. “The Qur'an was sent down to them. And they are more knowledgeable concerning the revelation than you, and it was revealed amongst them. And none of them are among you.” (Ibn Abbas pointed to the fact that not one Companion was among the Khawarij.) So some of them said, “Let us speak with him and let us see what he says.” I said, “Inform me of that which you harbor against the son of the uncle of the Messenger of Allah (peace be upon him) and his son-in-law (Ali), the Muhajiroun and the Ansar.” They said, “Three issues.” I asked, “What are they?” They said, “As for the first of them, then he (Ali) has allowed men to judge in the affair of Allah, yet Allah said, ‘...The judgement is for none but Allah...' (Qur'an, 12:40) So it is not for men to be judges.” So I asked, “This is only one issue.” They said, “As for the other issues, then he fought his enemies, yet he did not take any prisoners or war booty. So if those whom he fought were disbelievers, then their imprisonment and war booty has been made lawful. And if they were believers, then fighting them is not permissible.” I said, “These are only two issues, so what is the third?” They said, “Indeed, he removed the title, ‘Leader of the Believers' for himself, so therefore he is the leader of the disbelievers.” I said, “Do you have anything besides this?” They said, “This is sufficient for us.” So I said to them, “Do you hold that if I recite to you from the Book of Allah and the Sunnah of His Messenger (peace be upon him), that which refutes your statement, that you will obey?” They said, “Yes!” So I said, “As for your statement that he has allowed men to judge concerning the affair of Allah, then I shall recite to you that which shows that Allah relegated His judgement to men. Allah the Mighty and Majestic has said concerning differences between the woman and her husband, “If you fear a breach between the twain (the man and his wife), appoint (two) arbitrators, one from his family and the other from hers; if they both wish for peace, Allah will cause their reconciliation. Indeed Allah is Ever All-Knower, Well-Acquainted with all things.” (Qur'an, 4:35) So Allah made the judgement of the men a tradition to be believed in. So do you leave this (issue)?” They said, “Yes!” Ibn Abbas continued, “As for your statement that he fought and he did not take prisoners, nor did he take war booty, then do you revile your mother, Ayesha? Then you must declare her lawful in that which you have declared lawful with regards to other than her! So if you were to do that, then you would become disbelievers, as she is your mother. And if you were to say that she is not our mother, then you have disbelieved. Since, Allah says, ‘The Prophet is closer to the Believers than their ownselves, and his wives are their mothers...' (Qur'an, 33:6) “So you are revolving around two positions of misguidance. Regardless of which of them you adopt, you have adopted misguidance.” So they began to look at each other. I said, “Do you recant this position?” They said, “Yes!” “And as for your statement, that he removed the title of ‘Leader of the Believers' from his name, then I shall come to you with one whom you are pleased with and I shall see you. Indeed, you have heard that on the day of Al-Hudaybiyyah, the Prophet (peace be upon him) made a treaty with Suhayl Bin Amr and Abu Sufyan Ibn Harb. “So the Messenger of Allah (peace be upon him) said to the Leader of the Believers (Ali), ‘Write, O Ali: These are the terms of peace agreed upon by Muhammad the Messenger of Allah.' So the pagans said, ‘No, by Allah! Had we known that you were the Messenger of Allah, we would not have fought you.' “So the Messenger of Allah (peace be upon him) said, ‘O Allah! You know that I am the Messenger of Allah. Write O Ali: These are the terms of peace agreed upon by Muhammad Bin Abdullah.' (Al-Bukhari and Muslim) “So by Allah, the Messenger of Allah was better than Ali, yet he was not removed from Prophethood when he erased the title from his name.” Abdullah Bin Abbas then said, “So two thousand of those people repented, and the rest were killed for misguidance.” – This incident has been related in Musnad Ahmad (1/342), An-Nasa'i in Khasa'is Ali (no. 190), Al-Bayhaqi in Sunan Al
