Shaykh Saalih Al-Fawzaan (hafidahullah) was asked:

Is there present in this present time, those who carry the ideology of the Khawaarij (renegades)?

He (Hafidahullah) replied:

“Yaa Subhaanallah (Far removed is Allah from every imperfection)! This is present right now, are these not the actions of the Khawaarij?

Excommunicating Muslims (from Islaam) and worse than that, killing of Muslims; attacking them with bombs; this is the methodology of the Khawaarij.

And it comprises of three affairs:

Firstly: Excommunicating Muslims from Islaam.

Secondly: Exiting from obedience of the (Muslim) ruler.

Thirdly: Making permissible the blood of the Muslims. (i.e. allowed to kill them).

This is the methodology of the Khawaarij and even if an individual only believes this in his heart, and does not speak about it, nor act on it, he has still become a Khaarijee (renegade), due to his Aqeedah and opinions, which have not been openly expressed by him.”(1)

(1) Shaykul Islaam ibn Taymiyyah (rahimahullah) said about the characteristics of the Khawaarij:

“Then indeed there is none more harmful upon the Muslims than them; neither the Jews nor the Christians; for indeed they strived in killing every Muslim that did not agree with their view, declaring the blood of Muslims, their wealth and slaying of their children lawful, whilst making takfeer of them, due to their ignorance and innovations that caused to stray.” Minhaaj As-Sunnah 248/5
http://dusunnah.com/wp-content/uploads/2016/08/Warning-Against-IS.pdf

Majority of the following is from a translation of our Ustaadh Abu Khadeejah (hafidahullah)

Imaam Al-Aajuree (rahimahullah) said:

“Neither the scholars of old nor of these times, ever differed about the Khawārij. They regarded them as an evil people who were disobedient to Allāh, the Mighty and Majestic, and His Messenger (sallallahu alaihi wa sallam) even though they prayed, fasted and exerted themselves in worship, and all of this was of no benefit to them, even though they were apparent in enjoining the good and forbidding the evil, and that did not benefit them because they are a people who interpret the Qur’aan based on what they desire and they bring extreme difficulty upon the Muslims. Verily Allah, the Mighty and Majestic, the Messenger of Allah (sallallahu alaihi wa sallam); the rightly guided caliphs; the companions and those who followed them in goodness, (Allah’s mercy on them) warned us from them.” Ash-Sharee’ah 325/1

For more information read following article:

http://www.abukhadeejah.com/isis-in-iraq-syria-ibn-kathir-died-774-ah-if-the-khawaarij-ever-gained-strength-in-iraq-and-syria-there-would-be-mass-killing/

Source: Al-Ijaabaat Al-Muhimmatu fil Mashaakil Al-Mulimma, page 12