والإيمان هو الإقرار باللسان والتصديق بالجنان . وجميع ما صح عن رسول الله صلى الله عليه وسلم من الشرع والبيان كله حق، والإيمان واحد وأهله في أصله سواء . والتفاضل بينهم بالخشية والتقى ومخالفة الهوى وملازمة الأولى.
62. Belief consists of affirmation by the tongue and acceptance by the heart. 63. And the whole of what is proven from the Prophet, upon him be peace, regarding the Shari`a and the explanation (of the Qur'an and of Islam) is true. 64. Belief is, at base, the same for everyone, but the superiority of some over others in it is due to their fear and awareness of Allah, their opposition to their desires, and their choosing what is more pleasing to Allah.
Two issues here: what exactly is iman, what are its integrals which are essential to it? Does iman increase and decrease?
Confession with the tongue and acceptance by the heart are different. Confirmation of the heart can never be removed, and if it is you lose your faith. Confession of the tongue can sometimes be dropped, i.e. you can outwardly express disbelief to save your life, according to the Qur`an. Confession of the tongue depends on acceptance by the heart. Confession is necessary (according to some) to be considered a Muslim and in that is as important as the heart. Iman can stand on its own in the heart, but not on the tongue. If someone has faith on his tongue, but not in his heart, that is nifaq. If one has faith inwardly, but refuses to profess it without any threat, he is committing kufr.
Iman in terms of its reality and essence is iqrar, confessing and believing in the Oneness of Allah, and the Prophethood, and accepting those things which are known to be part of Islam from Allah and His Messenger. The question is, how much of the faith is considered necessary for to be a Muslim? He must believe that which the general community of Muslims believe but does not need to delve deep into logic or other things. Some things which are required are Oneness of Allah, Prophethood, Resurrection, reward and punishment for deeds, salah and zakat being wajib, iman in angels, books of Allah, messengers of Allah. We must believe in angels in general, and the ones mentioned by Allah and His Messenger specifically; same goes for the Books, etc. Confession and confirmation are both integrals of iman, and both must be enacted for a person to be considered a true believer (with exceptions mentioned above). Some actions, even with faith in your heart, can be kufr. Such as wearing a cross – revering a purely religious symbol of other religions. If one dies in this state he may die as a kafir. If he repents and says the shahadah he is again a mu`min, but has the sin of the kufr. Some scholars, such as much of the Asha`irah, say that iman only confirmation of the heart; the confession of the tongue is just extra. Others made iman three things: heart, tongue, and good actions. The Khawarij held this opinion, and said that one does not pray or fornicates becomes a kafir. Ahl ul-Sunnah says that action is important, but your iman will not be removed immediately if you do one of these actions. The Mu`tazilah say that if you commit one of these actions you are outside of iman, but not a kafir. Others, the Karamiyyah, say that only confession of the tongue and not the heart is a believer who goes to Hell, but if you have both heart and tongue then you are a believer who is saved.
Imam Abu Hanifah, the majority of the scholars of the Ahnaf, the Maturidis, and the research scholars of the Asha’irah are of the opinion that conviction and confession are both part of iman. However, most Asha’irah say that it is only conviction in the heart. This is an apparent difference, but in reality there is no difference. The Asha’irah just look at it from the perspective that the only real integral is conviction, but it is not acceptable for one not to confess with the tongue. A Maturidi will also say that one who is forced will not have to confess with the heart. True iman is in the heart to be considered a believer by Allah, but confession of the tongue is necessary for humans to understand that you are a believer.
On the issue of increase and decrease of iman, the Maturidiyyah say it does not, while the Asha’irah say it does. However, this is only an apparent difference; the Maturidiyyah, when they say iman mean the basic tenets of faith, which is why Imam Abu Hanifah used to say “My iman is like Jibril’s iman” and “Iman does not increase or decrease”. The Asha’irah would of course agree with this, but by iman they mean the strength of conviction in these basic tenets of faith, and of course the Maturidiyyah would agree with this. Imam Tahawi eloquently incorporates both opinions in point 64. He relates the debate to taqwa and how much one is able to avoid the haram. That is how people differ. The majority of Asha’irah say that iman increases and decreases, but some, like Imam al-Haramayn Juwayni, agreed with the Maturidi position.