Ibn Taymiyya (ra) said: “There is the essence of iman and there are its consequences. Kufr is opposed to iman in both respects. The essence of iman is belief (tasdiq) and confession (iqrar) and the actions of the heart or the body are its consequences. The opposite of iqrar and tasdiq which is the essence of iman is the rejection (kufr) of Allah and what He has said, and the refusal to believe (tasdiq) in Him and His words. The opposite of iman which is action and not confession is the kufr on account of which one does not go out of the millah but a kufr which renders the actions worthless…
Muhammad Ibn Yahya Ibn Rafii narrates from Abdurrazzaq from Mamar from Ibn Tawus and he from his father that when Ibn Abbas (ra) was asked about the words: “Those who fail to judge in terms of what Allah has revealed are unbelievers (kafirun).” (al-Maida 5/44) he said that they were guilty of kufr on that account. Ibn Tawus adds that this does not mean that they are like those who deny Allah, His angels, His books and His messengers…In a different version of the tradition which Muhammad Ibn Yahya has narrated from Abdurrazzaq from Sufyan from a man and finally from Tawus we have it that Ibn Abbas said: “He is guilty of kufr but not in the sense that he goes out of the millah.” (Ibn Kathir, Tafsir al-Qur’an al-Azim, 2/61) Ibn Ishaq has said that Waki narrated from Sufyan from Ibn jurayj that Ata said that he was guilty of a lesser kufr, a lesser zulm and a lesser fisq.
Muhamamd Ibn Nasr says that what Ata has said is right; people do sometimes call an unbeliever (kafir) zalim, wrongdoer, just as they call a sinning Muslim zalim. There are different kinds of zulm, wrong acts. The perpetrator of one zulm may cease to be a Muslim, but the perpetrator of another zulm may not. On one occasion Allah has said: “It is those who believe and confuse not their belief with zulm.” (al-Anam 6/82); on another occasion He has said: “Verily, associating someone with Allah is a great zulm.” (Luqman 31/13) A hadith which is reported by Ibn Mas’ud (ra) says that when the words: “those who believe and confuse not their belief with zulm” (al-Anam 6/82) were revealed, sahaba were perturbed and said to him: “Who of us is there who has not done any zulm (wrong)! RasulAllah (saw) said: “This is not what is meant here. Have you not heard the words of a pious man (quoted in the Qur’an): “Verily shirk is a great zulm.” (Luqman 31/13) Zulm here means shirk.” (Muslim; Tirmidhi)
Muhammad Ibn Yahya narrates from Hajjaj Ibn al-Minhal from Hammad Ibn Salamah, from Ali Ibn Zayd from Yusuf Ibn Mahran that Ibn Abbas (ra) said that: “Whenever Umar Ibn al-Khattab (ra) entered his house, he would open the mushaf (Qur’an) and read a few verses from it. One day when he entered his house and began reading he came to the verse: “those who believe confuse not their faith with any zulm” (al-Anam 6/82) He put on his shoes, flung his sheet on his shoulders, and went to Ubayy Ibn Ka’b and said: Aba al-Mundhir, have you read the verse: “those who believe confuse not their faith with any zulm” (al-Anam 6/82) Don’t we commit zulm and many other things? Ubayy said: Amir al-Muminin this is not what is meant here. Allah has said: “Verily, shirk is a great zulm.” (Luqman 31/13) and this is what zulm means here.” (Ibn Kathir, Tafsir al-Qur’an al-Azim, 3/444)
Muhammad Ibn Nasr says that fisq likewise is of two kinds: one on account of which one goes out of the millah, and the other on account of which one does not. A kafir may be called fasiq, just as a Muslim may be called fasiq. Allah has said of Iblis that: “He defied (fasaqa ‘an) the command of his Lord.” (al-Kahf 18/50) This defiance was kufr on his part, as Allah has said elsewhere: “And those who defy and do wrong (fasaqu) their abode will be in the Fire.” (as-Sajdah 32/20) Obviously He (swt) is referring here to the unbelievers, for following these words He says: “Every time they wish to get away from there, they will be forced into it, and they will be told: Taste you the penalty of the Fire which you were wont to reject as false.” (as-Sajdah 32/20) Allah has also called the defiant among the Muslims fasiqun but He has not excommunicated them. For example: “And those who launch a charge against chaste women and do not produce four witnesses (to support their allegations) flog them with eighty stripes and reject their evidence ever after for such men are fasiqun.” (an-Nur 24/4); or: “If anyone undertakes to perform hajj during these (months) let there be no obscenity, nor wickedness (fusuq) nor wrangling in the hajj.” (al-Baqara 2/197) Scholars have said that fusuq here means sin (masiyah).
Now if zulm is of two kinds and fisq is of two kinds, kufr is also of two kinds. On account of one kufr, one goes out of the millah; on account of the other one does not. Similarly shirk is of two kinds: one is to associate someone (or something) with Allah and violate His unity, on account of which one goes out of the millah. The other shirk is riya, dissimulation. Allah has said: “Whoever expects to meet his Lord; let him work righteousness and admit no one as partner in the worship of his Lord.” (al-Kahf 18/110) In other words, he should not work righteousness to please someone else. It is this kind of shirk in action which is what is meant in the hadith: “Augury is shirk.” (Abu Dawud; Tirmidhi; Ibn Majah; Ahmad, Musnad)” (Fatawa, 7/324-329)