الحمد لله رب العالمين، وصلى الله وسلم على نبينا محمد وعلى آله وأصحابه أجمعين، أما بعد
Al-Haafidh Ibn Katheer (rahimahullaah) said when commenting on the Khawaarij at the time when they had gathered together to fight against the rightly guided Caliph ‘Ali bin Abee Taalib (radhiyallaahu ‘anhu):
“These types of people are from the most peculiar manifestation of the progeny of Aadam, so glory be to The One that diversified His creation as He Wished, and that had already preceded in His pre-ordainment.
Likewise how excellent is the saying of some of the Salaf regarding the Khawaarij, that they are mentioned in His saying, The Most High:
قُلْ هَلْ نُنَبِّئُكُم بِالْأَخْسَرِينَ أَعْمَالًا
الَّذِينَ ضَلَّ سَعْيُهُمْ فِي الْحَيَاةِ الدُّنْيَا وَهُمْ يَحْسَبُونَ أَنَّهُمْ يُحْسِنُونَ صُنْعًا
أُولَٰئِكَ الَّذِينَ كَفَرُوا بِآيَاتِ رَبِّهِمْ وَلِقَائِهِ فَحَبِطَتْ أَعْمَالُهُمْ فَلَا نُقِيمُ لَهُمْ يَوْمَ الْقِيَامَةِ وَزْنًا
((Say: Shall We tell you the greatest losers in respect of [their] deeds? Those whose effort is lost in the worldly life while they thought that they were working good deeds! Those are the ones who disbelieve in the signs of their Lord and the meeting with Him so their deeds have become worthless; so We will not assign any weight to them on the Day of Resurrection.)) (Al-Kahf: 103-105)
The intent; is to point out that these ignorant and astray ones, wretched as they are in statements and actions; their opinion united them upon departure (i.e. splitting away) from the midst of the Muslims; and so acted under mutual collusion upon marching to the townships in order to gain authority in them and to fortify themselves therein and to relay (i.e. communication) to their brethren and their likes – from amongst those that were upon their notions and ideology from the people of Al-Basrah and other than it – that they should loyally join them there – and hence their union should be therein.
So Zaid bin Hussain At-Taa-ee said to them: ‘you have no ability over the townships, for there are armies based there over which you do not have capability, and they will prohibit you from them. However; you should set an appointed meeting with your brethren at the bridge on the river Jawkhaa; and do not leave Kufa in groups – but rather leave individually; so that they should not notice you.’
So they wrote a general decree to those upon their ideology and their policy from the people of Al-Basrah and other than it and sent it to them so that they should join them in loyalty at the river in order for them to become a combined single hand against the people.
Then they departed; slipping through individually so that no one should come to know of them and so prevent them from leaving. So they departed from amid their fathers and their mothers and their uncles and their aunts and parted from all of their relations – believing due to their ignorance and their lack of knowledge and intellect that this affair is pleasing to The Lord of the earth and the heavens. Yet they failed to know that it is from the greatest of major sins and the deadly misdeeds and from the grave calamities and errors. Along with it being from that which Iblees (i.e. the devil) has made alluring to them as did their own souls that inclined towards evil.
So a group of them (the people) managed to prevent some of their offspring and their relations and their brethren and thus brought them back and reprimanded them. So from them were those that then resumed upon steadfastness; and from them were those that escaped after that to join up with the Khawaarij – thus being at loss until the Day of Resurrection.
The rest of them went to that place, and they were joined by those to whom they had written from the people of Al-Basrah and elsewhere – and so they all came together at Nahrawaan.”
(Taken from: Al-Bidaayah wan-Nihaayah vol 10 p.580-582)
 Nahrawaan is an extensive district situated between Baghdad and Waasit. It was at Nahrawaan that the Khawaarij were defeated in battle by the forces of ‘Ali bin Abee Taalib (radhiyallaahu ‘anhu) in the year 38H, the leader of the Khawaarij; ‘Abdullaah Ar-Raasibee and most of his companions were killed in this battle. (See: Mu’jam al-Buldaan vol 5 p.324-325 & Al-‘Ibr vol 1 p.32)