Response to those who say: "If you believe 'Jama'at Al-Dawlah' are Khawarij, then why don't you go fight them?"
Translation of extract from Sh. Abu Muhammad AL-Maqdisi's book "Rulings on fighting the Bughaat"
The evidential support for fighting the Bughaat is Surah Hujurat, verse 9:
وَإِن طَائِفَتَانِ مِنَ الْمُؤْمِنِينَ اقْتَتَلُوا فَأَصْلِحُوا بَيْنَهُمَا ۖ فَإِن بَغَتْ إِحْدَاهُمَا عَلَى الْأُخْرَىٰ فَقَاتِلُوا الَّتِي تَبْغِي حَتَّىٰ تَفِيءَ إِلَىٰ أَمْرِ اللَّهِ ۚ فَإِن فَاءَتْ فَأَصْلِحُوا بَيْنَهُمَا بِالْعَدْلِ وَأَقْسِطُوا ۖ إِنَّ اللَّهَ يُحِبُّ الْمُقْسِطِينَ
"And if two factions among the believers should fight, then make settlement between the two. But if one of them oppresses the other, then fight against the one that oppresses until it returns to the ordinance of Allah . And if it returns, then make settlement between them in justice and act justly. Indeed, Allah loves those who act justly."
There are several stories on the reason for this verse being sent down, among it is the Hadith of the Prophet Saw.
It has been narrated on the authority of Anas b. Malik that it was said to the Prophet (ﷺ):
Would that you approached Abdullah b. Ubayy (to persuade him to accept Islam). The Prophet (ﷺ) (accordingly) went to him, riding a donkey, and (a party of) Muslims also went (with him). On the way they had to walk over a piece of land affected with salinity. When the Prophet (ﷺ) approached him, he said: Do not come near me. By Allah, the obnoxious smell of your donkey has offended me. (As a rejoinder to this remark), a man from the Ansar said: By God, the smell of the donkey of the Messenger of Allah (ﷺ) is better than your smell. (At this), a man from the tribe of 'Abdullah got furious. Then people from both sides got furious and exchanged blows with sticks, hands and shoes. And then this verse was sent down upon them.
This verse is the evidential support for fighting those interpret falsely - and it was evidence for all those who fought them, wether it was the pure companions, the scholars or the righteous people
And this is because Allah swt. said : فَقَاتِلُوا الَّتِي تَبْغِي حَتَّىٰ تَفِيءَ إِلَىٰ أَمْرِ اللَّهِ
"Then fight against the one that oppresses until it returns to the ordinance of Allah"
So Allah swt. ordered that the oppresive group is to be fought, and this is obligatory (Wajib), and it is Fard Al-Kifayah, if it is fulfilled by a group of Muslims, it is uplifted from the rest. Because if they left it off, then the Bughaat would cause corruption upon the earth and they would corrupt the peoples religion and their worldly affairs.