Just as the bearing witness to the two testimonies and acting upon them are the conditions for the validity of Islam, there are beliefs and actions that also nullify one’s Islam. Sheikh Muhammad Bin Abdul Wahhab summarized them in 10 points (some additional verses have been added) as to what nullifies Islam:
1. Shirk (associating partners in the worship of Allah).
“Verily, Allah forgives not (the sin of) setting up partners in worship with Him, but He forgives whom He pleases other sins than that.” (Qur’an, 4:116)
“Verily, whosoever sets up partners in worship with Allah, then Allah has forbidden Paradise for him, and the Fire will be his abode. And for the wrongdoers, there are no helpers.” (Qur’an, 5:72)
2. Setting up an intermediary between oneself and Allah. The one who prays to, seeks intercession from and puts his reliance on intermediaries has blasphemed according to the consensus of the scholars.
“And they worship other than Allah that which neither harms them nor benefits them, and they say, ‘These are our intercessors with Allah.’ Say, ‘Do you inform Allah of something He does not know in the heavens or on the earth?’ Exalted is He above all that which they associate as partners with Him.” (Qur’an, 10:18)
3. Not considering polytheists as disbelievers or having a doubt concerning their disbelief or considering their way as correct.
“Whoever disbelieves in Taghut and believes in Allah, then he has grasped the most trustworthy handhold that will never break.” (Qur’an, 2:256)
4. Believing that some guidance other than the guidance of the Prophet (peace be upon him) is more complete or that another’s judgment is better than the Prophet’s (is also an act of disbelief). This would be like the one who prefers the rule and law of false gods (be they human or otherwise) to the Prophet’s rule and law.
“But no, by your Lord, they can have no Faith, until they make you (Muhammad, peace be upon him) as a judge in all disputes between them, and find no resistance against your decisions, and accept (the decisions) with full submission.” (Qur’an, 4:65)
5. Disliking anything the Prophet (peace be upon him) brought, even if one does’nt act upon it, is an act of disbelief.
“It is not fitting for the believing man nor for the believing woman, that whenever Allah and His Messenger have decided any matter, that they should have any other opinion.” (Qur’an, 33:36)
6. Ridiculing or joking about any part of the religion of the Messenger (peace be upon him) or its rewards or its punishments. The evidence for this is in the Words of Allah:
“Say: Was it Allah, or His signs or His Messenger that you were mocking? Make no excuse, you have disbelieved after you had believed.” (Qur’an, 9:65-66)
7. Performing magic. This includes those magical incantations that make one love or hate another person. Allah says in the Qur’an:
“But neither of these two (angels) taught anyone (such things) until they had said, ‘We are only for trial, so disbelieve not (by learning such magic from us).”’ (Qur’an, 2:102)
8. Assisting and supporting polytheists against Muslims.
9. Believing that some people are permitted to be free from the Law of Muhammad (peace be upon him), in the same way that Khidr was free from the law of Moses (peace be upon him).
10. Turning away from the religion of Allah, not learning it or applying it. Allah says:
“And who does more wrong than he who is reminded of the signs of his Lord, then he turns aside therefrom? Verily, We shall exact retribution from the sinners.” (Qur’an, 32:22)