Tirmidhi

Explanation 1:

By this is meant the final period of the Rightly Guided Caliphate (Khilafah Rashidah).
The duration of this caliphate is thirty years.
The emergence of the Khawarij occurred during the caliphate of Ali radi Allahu anhu.
When two years of the Rightly Guided Caliphate remained, Ali radi Allahu anhu fought them at the place of Nahrawan
and killed them.
Among the Khawarij were young and immature-minded people who fell prey to deceptive slogans.
And the prophecy of the Messenger of Allah sallallahu alayhi wa sallam is manifesting in every era; in today’s tumultuous times, its manifestation can be seen everywhere.
May Allah Ta’ala grant us correct understanding of the religion and protect us from all kinds of tribulations. Ameen.

Commentary:
(1)
Some scholars have interpreted “the last era” to mean the final period of the Rightly Guided Caliphate, because these Khawarij appeared during the caliphate of Ali radi Allahu anhu. It is possible that near the Day of Judgment, such people may also emerge who will fall into the same misguidances in which the Khawarij were involved.
And Allah knows best.

(2)
Innovation (bid‘ah), whether in creed or in practice, is evidence of lack of intellect.
It is as if only a person who does not understand the religion, or considers the religion to be deficient, invents or adopts innovation.

(3)
Deviant sects present such things in support of their misguidance that a person of little knowledge is deceived by them and considers these things to be strong proofs. However, if their supposed proofs are examined in the light of the Qur’an and Hadith, their error becomes clear.

(4)
The meaning of “not passing beyond their throats” with regard to the Qur’an is that they will recite the Qur’an with their tongues, but its effect will not reach their hearts, or their hearts will be deprived of the correct understanding of the Qur’an.

(5)
An innovator (mubtadi‘) considers only his self-invented statements and actions to be Islam, and thus he is deprived of the true Islam.
Just as an arrow that passes completely through a hunted animal—although it is said to have had contact with the animal, in reality, this contact is null and void.
Similarly, the connection of the Khawarij or other people of innovation with Islam is, outwardly, established because they profess the two testimonies (shahadatayn) and perform the actions of Muslims, but due to innovation, their good deeds become unacceptable and nullified, and thus their connection with Islam does not remain established.

(6)
People of innovation should first be advised and their errors clarified. If they still do not desist and begin to become a cause of misguidance for the general Muslims, then the Islamic government should treat them as rebels and, by force, put an end to their tribulation.
Ali radi Allahu anhu also first sent Abdullah ibn Abbas radi Allahu anhu to advise the Khawarij, as a result of which many among them understood and accepted the obedience of Ali radi Allahu anhu.
Those who persisted in rebellion were fought against. (al-Bidayah wa’l-Nihayah: 4/292)

(7)
To cooperate with the Islamic government in ending tribulation is a righteous deed, for which there is reward.