What is the ruling on following ISIS and similar groups?
Muslims are obliged to fight against ISIS and invite them to honor the obligation God has enjoined upon them towards their rulers. According to scholars, it is only permissible to fight them after trying to dissuade them from their ways.
Imam al-San`ani al-Kasani said:
When a ruler learns that the Kharijites are wielding their weapons and readying for war, he must apprehend and detain them until they renounce their ways and repent. This is because if they are left fee, they will sow corruption on earth. Hence, they must be prevented. However, the ruler must not fight them unless they initiate hostilities… but if he does not learn of this until they h ave encamped and are ready for war, he must invite them to observe justice and return to the congregation of the Muslims in the hope they will respond and accept the invitation as is the practice of ahl al-harb.
Imam Al-Nawawi said:
The scholars maintain: It is obligatory to fight the bughah [rebels]; they are not deemed disbelievers on account of their baghy [rebellion]. If a baghi [rebel] renounces his disobedience, his repentance is to be accepted and he is not to be killed. The Companions unanimously agreed that the bughah are to be fought.
The goal of fighting the Kharijites
The main goal of fighting the Kharijites is to make them submit to their Muslim rulers. Al-Kasani the Hanafi scholar said:
This is because fighting them is for the sake of repelling their evil, not for the evil of their polytheism since they are Muslims. Provided they do not direct their evil at anyone, they are not to be fought.
Al-Khatib al-Shirbini said:
This is because the purpose of fighting them is to return them to obedience. But if they persist, he [the ruler] is to advise and exhort them [to renounce their ways]. But if they stand their ground, he is to warn them of war because God the Almighty commanded us to first seek reformation before fighting.
The extent of the permissibility of joining ISIS and similar groups
From the above, it becomes evident that ISIS and similar groups are from the Kharijites against whom the Messenger of God (peace and blessing be upon him) warned us and ordered that they be fought. According to Islamic law, it is not permissible to join them or any other takfiri sect because they are transgressors and seceders. How can it be permissible to join them after rulers have been commanded to fight them and after the Messenger of God (peace and blessings be upon him) described them as the dogs of hellfire?
[For further reading on this topic see INSIGHT #8, publication of Dar al-Ifta al-Misriyya]
Dar al-Ifta al-Misriyya