Saudi cleric Sa'd Al-Shathri stated that ISIS members are apostates during an interview with the Saudi TV channel Majd TV on August 31, 2014. Sheik Al-Shathri added that ISIS members who are unable to leave the organization for fear of being killed should kill their commanders and comrades in order to be saved from the Hellfire.
Sa'd Al-Shathri: The organization known as "The Islamic State of Iraq and Syria" is fighting Allah and His Messenger. They sow corruption and act against Islamic law. They shut down mosques, kill Islamic scholars, and prohibit religious books and the hijab. They torture Allah's believing servants. Therefore, I'd like to highlight various legal rulings in this matter.
First, belonging to this organization constitutes a major sin. Belonging to this organization despite knowing its true nature constitutes apostasy. Members of this organization should leave it immediately. Since (ISIS) kills those who try to leave it, members should kill their unit commander, and as many ISIS members as possible. Perhaps Allah will forgive them for having joined ISIS.
Second, any ISIS member who is killed is not a martyr. We believe that he will go to the Hellfire, according to the shari'a.
Third, an oath of allegiance pledged to ISIS is null and void, and should not be adhered to. It is worthless.
Fourth, it is forbidden to cooperate with ISIS in any way, since this is considered a betrayal of Allah, His Messenger and the Muslims. It is forbidden to reach any agreement or truce with them.
Fifth, fighting them is one of the most important duties ordained by the shari'a. We hope that anyone who is killed while fighting ISIS for the sake of Allah will be considered a martyr.
Sixth, ISIS has followers and supporters in many countries, and therefore Muslim should disclose any information they have about them, and inform the authorities about anyone who works with them.
When a mother informs the authorities about her son, and then he spends years in prison until he returns to his senses – she is fulfilling her duty. This is better than joining ISIS, or being killed supporting these heretics. The same holds true for a wife informing on her husband, a sister on her brother, a neighbor on his neighbor. This is done out of love for the people they inform on.