Praise be to Allah, and may peace and blessings be upon the Messenger of Allah, to proceed:
The principle, ‘Whoever does not make takfeer of the disbeliever, is (himself) a disbeliever’ is a well-known principle, and is the third nullification of the nullifications of Islam, as mentioned by the Shaykh Muhammad bin ‘Abdul-Wahhab (رحمه الله) when he said, “The Third: Whoever does not do takfeer of the polytheists, doubts their disbelief, or corrects their creed, disbelieves”.
Except that this principle is not upon this generalisation, and there is explanation and elaboration to be done, which whoever ignores falls into great falsehood, by doing takfeer of the Muslims or by not doing takfeer of the original disbelievers [e.g. Jews, Christians, Atheists, etc]. This explanation is as follows:
Know, firstly, that the origin regarding this principle is not related to circumstances involving doing or saying what is disbelief, rather it is related to rejecting reports [i.e. ayat, ahadeeth, etc] and accepting them, so whoever leaves the disbeliever without doing takfeer of him, this would be considered a denial on his behalf of the reports that involve doing takfeer of him, and upon this, there is no doubt that the report regarding takfeer of him must be authentic and agreed upon, and there is no doubt that the one who leaves-off doing takfeer must be rejecting these reports. For the mukafirat [those things that make one a disbeliever], are not one, and falling into them also is not upon one level; to explain this matter, we have to distinguish and divide them into two:
The First Category: The Original Disbeliever
Like the Jew, Christian, Magian and other than them. Whoever does not do takfeer of these, doubts their disbelief, or corrects their creed, then he is a disbeliever by consensus as was mentioned by more than one of the people of knowledge. Because in this [action] is a rejection of [shar'ee] texts that mention the falsehood of other than the creed of the Muslims and the disbelief of whoever is not upon the religion of Islam.
The Second Category: The Apostate from Islam
This one is upon two divisions:
The First: Whoever announces his disbelief and his leaving of Islam to another religion like Judaism, Christianity, Atheism, then the ruling upon him is akin to the ruling upon someone from the aforementioned category.
The Second: The one who commits a nullification of Islam, except he still claims to be upon Islam, and that he isn’t a disbeliever by committing this nullification, then he is upon two categories as well:
1. Whoever does a manifest nullification of Islam, upon which there is consensus [that it is a nullification] like insulting Allah, the Mighty and Majestic, for example, then he is a disbeliever by consensus; whoever does not do takfeer of him is one of two, either:
i. One who affirms that insulting [Allah] is disbelief, that this action is disbelief, except that he desists from implementing this ruling upon a specific person due to a lack of knowledge or a doubt that the person had, and the likes, then this person is wrong, and this statement of his is falsehood, however one cannot do takfeer of this person because he has not rejected nor denied any reports, as he has affirmed that the consensus that the one who insults [Allah] is a disbeliever.
ii. The one who denies that insulting Allah is disbelief in the first place, after explaining to him, because he rejects the consensus and the reports. The likes of these are the ones who worship the graves and attribute themselves to Islam. So whoever denies that this man’s action is disbelief, then he is a disbeliever because he has rejected the explicit texts and the consensus, but whoever affirms that this action is disbelief [i.e. the worshipping of the grave], but does not do takfeer of the person due to a doubt he sees, then he does not disbelieve.
2. The one who does a nullification of Islam upon which there is a difference of opinion, like the leaving-off of prayer, this issue for example, there is difference of opinion over, and the one who differs with another on this issue [whether it is disbelief or not] is not a disbeliever, nor even an innovator or fasiq, even if he is wrong.
[The one who totally leaves of prayer however, and does not pray in a whole year, except eid or the Friday prayers, is a disbeliever, the Shaykh is talking about the one who misses some prayers on a regular basis, and Allah knows best].
This is a summary of what I have concerning this principle.
May Allah send His peace and blessings upon Muhammed.
Shaykh Nasir bin Hamad al-Fahd, 10/5/1423.