Nullifiers of the two testimonies

Nullifiers of the two testimonies are the nullifiers of Islam because it is the two testimonies that one pronounces in order to enter Islam. Uttering the two testimonies is affirming their intent, and being steadfast in establishing their prerequisites like fulfilling the rituals of Islam. If one forsakes this steadfastness then he has invalidated the pledge he took when he uttered the two testimonies. 

The nullifiers of Islam are many and the scholars have collected them in books of Fiqh under the title, 'The Chapter of Riddah (Apostasy).' However, the most important of them are ten, which have been mentioned by Shaikhul-Islam Muhammad Ibn Abdul Wahhab (rahimahullah) (they are the following).

1. Shirk in the worship of Allah. Allah says, “Verily! Allah forgives not (the sin of) setting up partners in worship with Him, but He forgives whom he pleases - sins other than that...” [Soorah an-Nisa (4): 116] and, “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 Zalimoon (polytheists and wrongdoers) there are no helpers.” [Soorah al-Maida (5): 72] and it includes sacrificing for other than Allah, like tombs and jinn. 

2. Setting up intercessors between oneself and Allah, invoking them, asking them for intercession and relying upon them. One who does this is considered by consensus a disbeliever.

3. He who does not declare the Mushrikeen (those who associate partners in worship with Allah) to be disbelievers, or doubts their disbelief, or approves their Madhhab (faith, creed) has disbelieved (in Allah). 

4. Believing that the guidance of someone other than the Prophet is more complete than his guidance, or that the ruling of other than him is better, like those who prefer the ruling of the tawagheet (pl. of Taghoot meaning things worshiped other than Allah) over the ruling of Allah's Messenger and they prefer manmade laws to Islam. 

5. He, who hates something from that which the Messenger came with, has disbelieved, even if he was acting upon it. 

6. He, who mocks at something from the Religion of the Messenger, its rewards or punishments, has disbelieved. The proof of this is the Saying of Allah, “Say, 'Was it at Allah, and His Ayat and His Messenger that you were mocking? Make no excuse, you have disbelieved after you had believed.” [Soorah Tawbah (9): 65-66] 

7. Magic. From the types of magic is that which causes unity and disunity among people (like causing separation of the husband from his wife or causing him to love her). He, who does this or is pleased with it, has disbelieved. The proof is the Saying of Allah, “...but neither of these two (angels) taught anyone (such things) until they had said, 'We are only for trial, so disbelieve not (by learning this magic from us).'” [Soorah al-Baqarah (2): 102]

8. Aiding and cooperating with the Mushrikeen (disbelievers) against the Muslims. The proof is the Saying of Allah, “If any amongst you takes them as Awliya, then surely he is one of them. Verily, Allah guides not those people who are the Dhalimoon (polytheist and wrongdoers and unjust).” [Soorah al-Maidah (5): 51] 

9. He, who believes that some people can be excused from the Sharee'ah of Muhammad , just like Khidr was not liable to the Sharee'ah of Moosa , is a disbeliever.

I (i.e., Shaikh Saleh al-Fawzan) say, 'this is just like what the extremist Sufis believe that they reach a stage (through their piety), where they are not in need of following the Messenger.

10. Turning away from the religion of Allah, neither learning it, nor acting upon it. The proof is the Saying of Allah, 'But those who disbelieve, turn away from that whereof they are warned.” [Soorah al-Ahqaf (46): 3] “And who does more wrong than he, who is reminded of the Ayaat (proofs, evidences, verses, lessons, signs, revelations, etc.) of his Lord, then he turns aside therefrom? Verily, We shall exact retribution from the Mujrimoon (criminals, disbelievers, polytheist, sinners, etc.).” [Soorah as-Sajdah (32): 22] 

Shaikhul-Islam Muhammad Ibn Abdul Wahhab (rahimahullah) said,

“There is no difference if one does any of them (the above nullifiers) jokingly, seriously or in fear, except under force. They are all very dangerous and most likely to happen. So, it is necessary for a Muslim to be aware of them, and fear them for himself. And we seek Allah's protection from that which brings about His Anger and severe punishment.”