Question: It is stated in a hadith-i sharif that no sin causes kufr (disbelief) except shirk (polytheism). Apart from shirk, there are also sins that cause disbelief, as is known. Then what is the meaning of shirk that is mentioned in this hadith-i sharif?
ANSWER
Shirk means attributing partners to Allahu ta'ala. A person who does the attributing is called a mushrik (polytheist). There are kinds of disbelief. The worst, the gravest kind is shirk. It has been a generally accepted rule that when several subjects are to be referred to under one common nomenclature, the gravest one is mentioned. For this reason, the word shirk used in Qur'anic verses and hadith-i sharifs comprehends all sorts of disbelief.

The Qur'an al-karim says (what means):
(Allahu ta'ala never forgives shirk [all sorts of disbelief]. He forgives [all] sins [venial or grave] except shirk if He wills.) [An-Nisa' 48]

As a disbeliever becomes a Believer by saying Kalima at-Tawhid once, so a Believer becomes a disbeliever by saying one word. He who says something that causes disbelief will lose his faith without even noticing it. A hadith-i sharif says:
(A time will come that a person will lose his faith without even noticing it. Faith will go out of him as a shirt is taken off.) [Daylami]

Whoever falls into disbelief, rewards (thawab) of all of his acts of worship will become null and void. If he repents, they will not be returned. He must renew his nikah, too. It is not enough only to say the Kalima ash-Shahadah for repentance. Repentance for the thing that caused one's apostasy is required, too. If he does not know the things that caused him to fall into disbelief, it is enough to say, "I repent of all my statements and actions that caused disbelief."

It is written in the books Bariqa, Hadiqa, and Majma'ul-anhur:

"If a Muslim, male and female alike, makes a statement or commits an act [consciously and without being subjected to duress] that he or she knows Islamic scholars unanimously define as one of the statements or acts that will cause one to become a disbeliever, he or she will lose his or her faith (iman) and become a murtad (apostate), even if the statement has been made or the act has been committed for a jocular purpose or without really thinking of its meaning. This sort of disbelief is termed kufr-i-inadi [disbelief out of obstinacy]. It causes one to become an apostate, to do so purposely, even if one does not know that the statement or the act concerned causes a state of disbelief. In this case the state of disbelief lapsed into is called kufr-i-jahli [disbelief out of ignorance] because it is fard for every individual Muslim to learn those Islamic facts that they have been enjoined to know. Not to know them, therefore, is a grave sin, instead of an excuse. People who have lost their faith by way of kufr-i-inadi or kufr-i-jahli will also lose their nikah (state of being married according to Islam’s canonical code). What a male Muslim, who has in this way lost his nikah, has to do is, getting a verbal proxy from his wife first, renew his nikah through a process termed tajdid-i-nikah, which is performed in the presence of two (male Muslim) witnesses or among the congregation in the mosque. Hulla is not necessary for tajdid (renewal of nikah) that a Muslim has had to perform more than twice. If a Muslim makes a statement causing a state of disbelief by mistake or in an interpretable way or under duress, he will neither become an apostate nor lose his nikah. If a person consciously makes a statement that is a matter of disagreement among the Islamic scholars as to whether it should be listed with acts causing a state of apostasy, he will not become an apostate, but he should make repentance, seek forgiveness, and renew his nikah for a margin of safety.”

(When a person falls into disbelief in either of the two ways [kufr-i inadi or kufr-i jahli], his previous acts of worship will become null and void. They are not returned even if he makes repentance. If he is rich, he has to perform the hajj again. It is not necessary for him to reperform his previous salats, to fast again, or to pay again the zakat he gave. It is not enough only to say the Kalima ash-Shahadah for repentance. Repentance for the thing that caused one's apostasy is required, too. If a person makes a statement causing a state of disbelief by mistake or in an interpretable way or if he consciously makes a statement which is a matter of disagreement among the Islamic scholars as to whether it should be listed with acts causing a state of apostasy, he will not become an apostate. But he had better renew his faith.)

Who is called a kafir?
Question: The word kafir (disbeliever) is used to refer to a person who disbelieves in Allah. Are the Ahl al-Kitab, who believe in the existence of Allah, called kafirs?
ANSWER
According to Islam, people are divided into two groups:
1. Those who are Muslims,
2. Those who are not Muslims.

Those who are not Muslims are called non-Muslims or kafirs. Kafirs, too, are divided into two groups:
1. Those with a holy book [Ahl al-Kitab],
2. Those without a holy book.

Christians and Jews are kafirs with a holy book. Atheists, polytheists, Buddhists, Zoroastrians, and those who believe in other religions are kafirs without a holy book. All kafirs, with or without a holy book, will go to Hell.

All of the Ahl al-Kitab, that is, Christians and Jews, will go to Hell. As a matter of fact, some Qur'anic verses say (what means):
(Certainly, all disbelievers, be they from among the Ahl al-Kitab [Jews and Christians] or from among polytheists, will be in the fire of Hell. They will abide therein eternally. They are the worst of creatures.) [Al-Bayyinah 6]

(Those who say "Allah is the Messiah, son of Mary" have become disbelievers. But the Messiah said, "O children of Israel, worship Allah, who is my Lord and your Lord. Know that whoever ascribes partners to Allah, Allah forbids Paradise to him. His abode is the Fire, and there are no helpers for the unjust.") [Al-Ma'idah 72]

(O you who believe! Do not take the Jews and Christians as your friends. They are the friends of one another [in their enmity toward Islam]. Whoever takes them as his friends becomes one of them [a disbeliever]. Allah does not guide the unjust people [who wrong themselves by taking disbelievers as their friends].) [Al-Ma'idah 51] (If the People of the Book were on the true path, would he who takes them as his friends have been called a disbeliever?)

(Fight those of the people given the Book who do not believe in Allah and the Day of Judgment, who do not consider forbidden that which Allah and His Messenger have forbidden, and who do not follow the true religion [Islam], until they give the jizya with their own hands in a state of humiliation [in submission].) [At-Tawbah 29]

(Those who deny Our aayaat are disbelievers. They are the dwellers of Hell; they will remain therein eternally.) [Al-Baqarah 39] (All non-Muslims are disbelievers because they deny Qur'anic verses.)

(Those who disbelieve in Our aayaat and thus become disbelievers, We will soon make them enter the Fire.) [An-Nisa' 56]

Is shirk termed a sin?
Question: In the books İslam Ahlakı and Cevap Veremedi, it is written that seven major sins are as follows: (1) shirk; (2) killing someone; (3) practicing sorcery; (4) appropriating the property of an orphan; (5) accepting or giving interest; (6) deserting the combat area when one is face to face with the enemy; (7) slandering chaste women. Why is shirk classed among major sins? Isn't a sin different from kufr (disbelief)?
ANSWER
A sin or haram means rebelling against Allahu ta'ala and transgressing what He has forbidden. Surely the gravest of these prohibitions is shirk and disbelief. Therefore, shirk and disbelief are classed among the major sins. It means that they are the gravest forms of rebellion. Our Master the Prophet, too, mentioned shirk under the heading of "major sins." This means to say that both shirk and disbelief have been included in the forbidden things. Some people fail to understand this subtlety and criticize Islamic books.

Does a cross become a Muslim?
Question: Some people claim, "If a Muslim wears a cross around his neck and wraps around his waist a robe girdle called zunnar that is worn by priests and if he lays prostrate or performs salat in this state, the cross and the robe girdle will become Muslims. From then on, there is nothing wrong with performing salat with them. So is the case with all objects that are signs of disbelief." Is it possible that a cross and a robe girdle become Muslims? If one puts a bottle of wine into one's pocket and performs salat with it, does the wine become a Muslim?
ANSWER
A cross and zunnar are signs of disbelief. They are not exempted from being signs of disbelief by laying prostrate or washing them with Zamzam. It is disbelief, too, to use a cross, a robe girdle called zunnar that is worn by priests, or other signs of disbelief when one performs salat. A salat performed with wine in one's pocket is not valid, and this wine does not become a Muslim.

Idolatry and shirk
Question: Polytheists, too, know that idols are not creative. They only make idols intermediaries to approach Allah. Such people become polytheists, but why do those who make the Awliya' intermediaries to approach Allah not become polytheists?
ANSWER
It is very ugly to liken the Awliya' to idols.

Muslims do not worship prophets or Awliya'. They know that they are not companions or partners of Allahu ta’ala. They believe that they are creatures and human beings and that they are not worth worshiping. They have the belief that they are the beloved slaves of Allahu ta’ala, and He will pity His slaves for the sake of His beloved ones. They say, "Allahu ta’ala alone creates loss and profit. He alone is worth worshiping. He pities His slaves for the sake of His beloved ones." As for polytheists, though they say that their idols are not creative, they believe that their idols are worth worshiping, and so they worship them. Because they say idols are worth worshiping, they become polytheists. Otherwise, they would not become polytheists for saying that they wanted intercession. Expecting intercession from idols is, without doubt, a false belief. Though such a belief is impermissible and false, it is not shirk. What is shirk is worshiping idols. (The Sunni Path)