We know that the opposite of belief in Allah is disbelief in Allah. There is major and minor disbelief. Major disbelief contradicts the core of faith, whereas minor disbelief contradicts the perfect state of faith. Major disbelief takes one out of the fold of Islam, and Allah does not accept from its perpetrator any ransom or compensation. Allah, the Exalted, says: {And whoever desires other than Islam as religion - never will it be accepted from him, and he will be in the Hereafter among the losers.} [Surat Āl ‘Imrān: 85] He Almighty also says: {Those who disbelieve and die as disbelievers, even an earth full of gold will never be accepted from any of them, if offered as ransom. For such people there will be a painful punishment, and they will have no helpers.} [Surat Āl ‘Imrān: 91] And He, Exalted be He, says: {And fear a Day when no soul will avail another anything, nor intercession will be accepted, nor compensation taken, nor will they be helped.} [Surat al-Baqarah: 48] Disbelief renders all good deeds worthless. Allah Almighty says: {Whoever rejects the faith, all his efforts will be worthless and in the Hereafter he will be among the losers.} [Surat al-Mā’idah: 5] Commenting on the verse {Whoever rejects the faith, all his efforts will be worthless}, Ibn ‘Abbās (may Allah be pleased with him) said: "Allah Almighty informs that faith is the firmest bond and that He does not accept any deed without it and does not forbid Paradise except to those who reject it." [Narrated by At-Tabari (3/113), (9/593) and Ibn Abi Hātim in At-Tafsīr (1307), yet in his commentary on: {If they believe as you have believed.}]
The disbeliever will dwell in Hellfire eternally. Allah, the Exalted, says: {Those who disbelieve and do wrong, Allah will not forgive them nor will He guide them to a way, except the way of Hell, abiding therein forever. And that is easy for Allah.} [Surat an-Nisā’: 168-169]
Major disbelief has various kinds, which Allah Almighty mentioned in His Book, and He Almighty stated that the disbelief of disbelievers may sometimes be Johūd (rejection), like in the verse that says: {We know well that what they say grieves you [O Prophet]. It is not you that they doubt, rather it is the verses of Allah that the wrongdoers deny.} [Surat al-An‘ām: 33] In another verse, He Almighty says: {But none rejects Our signs except every ungrateful treacherous.} [Surat Luqmān: 32] And He, Glorified be He, says: {They denied them wrongfully and arrogantly, although their hearts were convinced that they were true. See then how was the end of those who spread corruption!} [Surat an-Naml: 14]
And their disbelief sometimes takes the form of abandonment and arrogance towards the truth. About Satan, the leader of disbelievers, Allah Almighty says: {And when We said to the angels, “Prostrate before Adam,” and they prostrated except Satan; he refused and was arrogant, and was one of the disbelievers.} [Surat al-Baqarah: 34] Noah (peace be upon him) is quoted in the Qur'an as saying: {Every time I call them so that You may forgive them, they thrust their fingers into their ears and cover their faces with their garments, and persist in obstinacy and grow extremely arrogant.} [Surat Nūh: 7]
At other times, disbelief takes the form of Takdhīb (denial). Regarding the previous nations, Allah Almighty says: {[Their] case is like that of the people of Pharaoh and those before them. They all denied Our signs, so Allah seized them for their sins, for Allah is severe in punishment.} [Surat Āl ‘Imrān: 11] Allah Almighty also says: {Rather, the disbelievers persist in denying it.} [Surat al-Inshiqāq: 22] It makes no difference whether the denial is expressed by the tongue or by the heart. About the hypocrites, Allah Almighty says: {Have you not seen the hypocrites who say to their fellow disbelievers from the People of the Book: "If you are expelled, we will surely leave with you, and we will never obey anyone concerning you, and if you are attacked, we will surely come to your aid." But Allah bears witness that they are truly liars.} [Surat al-Hashr: 11] He Almighty also says: {When the hypocrites come to you, they say, "We bear witness that you are indeed the Messenger of Allah," And Allah knows that you are indeed His Messenger, and Allah bears witness that the hypocrites are truly liars.} [Surat al-Munāfiqūn: 1]
Disbelief sometimes takes the form of Shakk (doubt and suspicion), as the person is hesitant and unsure about the truth, the Resurrection, and the meeting with Allah Almighty. In a Qur'anic story, the owner of a garden said: {Nor do I think that the Hour will ever come. Even if I am brought back to my Lord, I will surely find something better than this.} [Surat al-Kahf: 36] In response, his believing companion said to him: {Do you disbelieve in He Who created you from dust, then from a sperm-drop, then fashioned you into a well proportioned man?} [Surat al-Kahf: 37]
At other times, disbelief takes the form of cursing and mockery. About the disbelievers, Allah, the Exalted, says: {And there were messengers before you [O Prophet] who were ridiculed, but those who mocked them were overwhelmed by what they used to ridicule.} [Surat al-An‘ām: 10] And about the people of Noah and their mockery of him, Allah, Exalted be He, says: {So he started constructing the Ark, and every time some chiefs of his people passed by him, they ridiculed him. He said, “If you ridicule us now, we will soon ridicule you as you are ridiculing us.} [Surat Hūd: 38]
Disbelief may sometimes take the form of turning away and barring access to the way of Allah Almighty, Who says: {Or have they taken other gods besides Him? Say: "Bring your proof. Here is the Book of those who are with me, and the Book of those who came before me." Yet most of them do not know the truth, so they turn away.} [Surat al-Anbiyā’: 24] And He, Blessed and Exalted be He, says: {We have not created the heavens and earth and all that is between them except for a true purpose and for a set term, yet those who disbelieve turn away from what they have been warned of.} [Surat al-Ahqāf: 3]
And sometimes disbelief is hatred of the truth. Allah Almighty says: {That is because they detest what Allah has sent down, so He rendered their deeds worthless.} [Surat Muhammad: 9]
We know that there is a minor disbelief, which is less than the major one. Minor disbelief does not contradict the core of faith, yet it contradicts its perfect state. Minor disbelief does not take a person out of the fold of Islam, nor does it cause him to dwell in Hellfire eternally or render all his deeds worthless. There are numerous forms of minor disbelief.
Another form lies in the Hadīth in which the Prophet (may Allah’s peace and blessings be upon him) said: "Cursing a Muslim is evil doing, and fighting him is disbelief." [Narrated by Al-Bukhāri (48), Muslim (64), At-Tirmidhi (1983), An-Nasā’i (4108), and Ibn Mājah (69)] Another form lies in the Hadīth in which the Prophet (may Allah’s peace and blessings be upon him) said: "Two things are found among people which are tantamount to disbelief: libeling the lineage and wailing over the dead." [Narrated by Muslim (67)] The Prophet (may Allah's peace and blessings be upon him) also said: "Do not revert to disbelief after me by striking the necks of one another." [Narrated by Al-Bukhāri (121), Muslim (65), An-Nasā’i (4131), and Ibn Mājah (3942)]
However, such disbelief does not bring one out of the fold of Islam or cause him to languish eternally in Hellfire, for Allah Almighty calls the believers who fight one another as brothers. He, Exalted be He, says: {If two groups of the believers fight one another, make peace between them} [Surat al-Hujurāt: 9-10] So, He calls them believers even though they fight each other. After citing a group of such Hadīths, Imām Ahmad (may Allah have mercy upon him) said: "These Hadīths cited above: 'There are three traits, whoever has them is a hypocrite' affirms the sinfulness of the mentioned traits. We relate these Hadīths as they are and do not interpret them. The same applies to similar Hadīths, which are reported authentically and recorded. We yield to them, even if we do not know their interpretation. No one should dispute them or argue about them. Such Hadīths should only be interpreted in the way they were reported." [Sharh Usūl I‘tiqād Ahl As-Sunnah Wa Al-Jamā‘ah (1/182)]