Evidence from the Noble Quran

A number of evidence have been conveyed in the Quran which indicate that the Imaan of a person increases and decreases, from them:
1-   The Statement of Allah the Exalted: The ?true? believers are only those whose hearts tremble at the remembrance of Allah, whose faith increases when His revelations are recited to them, and who put their trust in their Lord. Al-Anfaal :2 Ash-Shanqeetee commented on this ayah by saying, “This ayah is explicit in the increasing of Imaan, and the Exalted has made that clear in other places, as well … These ayaat also indicate through necessary inference that Imaan also decreases, for everything that increases also decreases.” [64] “Adwaa’ al-Bayaan fi Idhah al-Qur’an bil-Qur’an” (2/50)
2-   The Statement of Allah, the Exalted: Whenever a surah is revealed, some of them ask ?mockingly?, “Which of you has this increased in faith?” As for the believers, it has increased them in Imaan, and they rejoice. But as for those with sickness in their hearts, it has increased them only in wickedness upon their wickedness, and they die as disbelievers.  at-Tawbah :124-125
Ibn Katheer commented on this ayah by saying, “This ayah is from the greatest signs that Imaan increases and decreases, as was the opinion the majority of the righteous predecessors and their successors from the renowned scholars, rather more than one reported that there was consensus upon that.” [65] “Tafseer al-Qur’an al- ‘Adhim” (4/239)
3-   The Statement of Allah the Exalted: He is the One Who sent down serenity upon the hearts of the believers so that they may increase even more in their faith. To Allah ?alone? belong the forces of the heavens and the earth. And Allah is All-Knowing, All-Wise. Al-Fath :4
Ash-Shanqeetee said, “This noble ayah indicates that Imaan increases, which has also been indicated by other ayaat from the Book of Allah…and the truth in which there is no doubt is that Imaan increases and decreases, which is the view that the people of Sunnah are upon. This has been indicated by divine revelation in the Quran and the Sunnah.” [66] “Adwaa’ al-Bayaan” (7/394)


Evidence from the Sunnah
There are numerous hadeeths that indicate that Imaan increases and decreases, from them:
1-   On the authority of Aboo Hurayrah (may Allah be pleased with him) that the Prophet ? said, “A fornicator is not a believer at the moment of their fornication, nor is a thief a believer at the moment of their theft, nor is a person drinking wine a believer at the moment of their drinking it, nor is a robber a believer at the moment of their robbery while the people are looking on at him.” [67] Reported by al-Bukhaaree (2475) and Muslim (75) with a slight variation
As can be noted, the Prophet ? negated the perfection of their mandatory Imaan because of these major sins they have carried out, which indicate that their Imaan decreases because of these sinful actions.

An-Nawawi said, “The correct opinion which the verifying scholars are upon, is that the meaning of this is that they do not commit this act of disobedience while having complete Imaan. And this is from the terms that is used in negating a thing and what is meant by it is negating its completion and what is desired from it, like how it is said (There is no knowledge except that which benefits, and there is no wealth except in the ownership of camels, and there is no life except the life of the afterlife.)” after which he said, “That and the consensus of the people of truth that the fornicator, the thief, the murderer, and their likes from those who commit major sins, with the exception of polytheism, that they are not excommunicated from Islam because of these sins, rather they remain believers who are deficient in their Imaan.” [68] “al-Minhaj fi Sharh Saheeh Muslim ibn al-Hajaj” (2/41)
2-   Al-Bukhaaree gathered in his Sahih in the Book of Imaan, a Chapter on the varying ranks of the people of Imaan with regards to their actions, and he mentioned in it the hadeeth of Aboo Sa’eed (may Allah be pleased with him) attributed to the Prophet ? – where he said, “The people of paradise will enter paradise, and the people of the hellfire will enter the hellfire, then the Almighty will say “Take out whoever had in their heart Faith equal to the weight of a grain of mustard seed …” [69] Reported by al-Bukhaaree (22) and Muslim (184) with a slight variation And this indicates that had the least Imaan from among the believers. Had Imaan not increased nor decreased, then all the people of Imaan would be deserving of Paradise and they would be at the same level!

The statements of the Imams of the Ahl Sunnah regarding the increase and decrease of Imaan
The consensus that Imaan increases and decreases
Yahya ibn Sa’eed al-Qattan said, “Everyone I have met from the Imams would say, “Imaan is speech and action; it increases and decreases.”” [70] “Siyar A’lam an-Nubala’” (9/179)

Ahmad ibn Hanbal said while mentioning a number of his held beliefs, “Imaan is speech and action; it increases and decreases.” Then he mentioned some issues after which he said, “This is what the righteous predecessors of the scholars of all the lands have agreed upon.” [71] “Manaqib al-Imam Ahmad” – Ibn al-Jawzi (p. 222-224)

Al-Bukhaaree said, “I met more than one thousand men from the scholars in different regions, and I did not see a single one of them differ in that the Imaan is speech and action; that it increases and decreases.” [72] Ibn Hajr mentioned it in “Fat-h al-Baaree” (1/47), as did az-Zabidi in “Ithaf as-Sadah al-Muttaqin” (2/256)

Ibn Jareer said, “As for what is asked about Imaan; is it speech and action that increases and decreases, or is there no increasing of it nor decreasing? What is correct in this matter is the statement of those who say that “It is speech and action; it increases and decreases.” And that is what the reports have come with from a group of the companions of the Prophet ? – and it is what the people of religion and virtue have remained upon.” [73] “Sarih as-Sunnah” (25)

Ibn Taymiyyah said, “The righteous predecessors agreed that Imaan is speech and action; it increases and decreases.” [74] “al-Fataawa” (7/672)

The statements of the righteous predecessors and scholars regarding the increasing of Imaan and its decreasing
1-   ‘Abdullah ibn Mas’ood (may Allah be pleased with him) would say in his supplication, “O’ Allah increase me in Imaan, certainty, and understanding.” [75] Reported by at-Tabaraanee (9/109) (8549), and al-Bayhaqee in “Shu’ab al-Imaan” (46) and al-Aajoory in “ash-Sharee’ah” (218) and the text is from him. Al-Haythami elaborated on its chain of narration in “Mujma’ az-Zawa’id” (10/188)
2-   Jundab ibn ‘Abdillah al-Bajali (may Allah be pleased with him) narrated, “"We were with the Prophet (?), and we were strong youths, so we learned Imaan (Faith) before we learned Qur'an. Then we learned Qur'an and our faith increased thereby. [76] Reported by Ibn Maajah (61), at-Tabaraanee (2/165) (1678), and al-Bayhaqee (5498) with slight variations. Al-Albaanee authenticated it in “Saheeh Sunan Ibn Maajah” (61), as did al-Wadi’i in “as-Saheeh al-Musnad” (285), and al-Busayri authenticated its chain in “Misbah az-Zujajah” (1/12), and Shu’ayb al-Arna’oot said that the men of the chain are trustworthy in his edition of “Siyar A’lam an-Nubala’” (3/175)
3-   ‘Umayr ibn Habeeb al-Khatmi (may Allah be pleased with him) said, “Imaan increases and decreases.” It was said, “And through what is its increases and decreases?” He said, “If we remember Allah Almighty, praise Him, and glorify Him, then that would increase it. And if we are heedless, wasteful, and oblivious, then that would decrease it.” [77] Reported by ‘Abdullah ibn Ahmad in “as-Sunnah” (624), and Ibn Abi Shaybah (30963), and al-Khallaal in “as-Sunnah” (1582). Ibn Taymiyyah said in “Majmoo’ al-Fataawa” (7/224) that, “It has many well-known chains”
4-   ‘Alqamah ibn Qays an-Nakh’iee would say to his companions, “Walk with us so that we may increase in Imaan.” [78] Reported by Ibn Abi Shaybah (30999), and Abu Nu’aym in “Hilyatul-Awliya’” (2/99) and al-Bayhaqee in “Shu’ab al-Imaan” (57). Al-Albaanee said its chain is good in his edition of “al-Imaan” of Ibn Abi Shaybah (104).
5-   Al-Awzaa’ee was asked about Imaan, “Does it increase?” He said, “Yes, until it is like the mountains.” He was then asked, “And does it decrease?” He said, “Yes, until there is nothing left of it.” [79] Reported by al-Lakaa’ee in “as-Sunnah” (5/1030)
6-   Sufyaan ath-Thawree said, “Imaan increases and decreases.” [80] Reported by ‘Abdullah ibn Ahmad in “as-Sunnah” (1/310) and Ibn Battah in “al-Ibaanah al-Kubra” (2/852)
7-   Ash-Shaafi’ee said, “Imaan is speech and action; it increases and decreases.” [81] Reported by Abu Nu’aym in “al-Hilyah” (10/115), and al-Hakim in “Manaqib ash-Shaafi’ee” (like in al-Fath 1/47), and Ibn ‘Abd al-Barr in “al-Intiqaa’” (p.81), and al-Bayhaqee in “Shu’ab al-Imaan” (1/81) and in “al-I’tiqaad” (p.120) and in “Manaqib ash-Shaafi’ee” (1/385). An-Nawawi mentions it in “Tahdhib al-Asma’ wal-Lughat” (1/66), as did adh-Dhahabi in “as-Siyar” (10/32), and Ibn Hajr in “al-Fath” (1/47).
8-   ‘Abd ar-Razzaaq as-San’aanee said, “Ma’mar, Ibn Jurayj, ath-Thawree, Maalik, and Ibn ‘Uyaynah would say, “Imaan is speech and action; it increases and decreases.” [82] Reported by ‘Abdullah in “as-Sunnah” (1/343) and al-Aajoory in “ash-Sharee’ah” (2/606)
9-   Ahmad ibn Hanbal said, “Aspects of Imaan are better than other, it increases and decreases, and its increasing is through actions, and its decreasing is through forsaking actions, because the speech confirms its existence.” [83] Reported by al-Khallaal in “as-Sunnah” (3/581)

A clarification to Maalik abstention from stating that Imaan decreases.
It has been narrated from him that he would abstain from saying that Imaan decreases – and not the negation of it as some have misunderstood his words to mean – due to the lack of explicit evidence that reached him in this regard. When these narrations reached him at a later time, he asserted that Imaan decreases as well, as has been reported from him from numerous narrations.

It was also said that He had initially abstained from that, as the Quran only spoke of the increase in Imaan and made no mention its decrease. However, he later abandoned this, and it was reported from him the view that Imaan both increases and decreases, and this is what the people of knowledge know of him.
Ahmad ibn al-Qaasim said, “We discussed those who say “Imaan increases and decreases”, so Imam Ahmad mentioned a few names, then he said, “And Maalik ibn Anas says, “It increases and decreases.” I said to him, “It has been narrated regarding Maalik that he said, “It increases, but does not decrease.” He said, “Indeed it has been narrated from him that “It increases and decreases,” Ibn Naafi’ narrates it from Maalik.” I said to him, “Ibn Naafi’ narrates that from Maalik?” He said, “Yes.”” [84] Reported by al-Khallaal in “as-Sunnah” (3/592)

The narrations that have been transmitted from him about this are numerous, from them:
‘Iyaad said, “A few have said, “I heard Maalik say “Imaan is speech and action, it increases and decreases, and components of it are better than other.” [85] “Tarteeb al-Madaarik” (2/43)
Ibn Rushd said, “It has been narrated from Maalik may Allah have mercy on him, that he would express the view that Imaan increases, and would abstain from expressing that it decreases, since Allah the Exalted does not state anything other than its increasing in the Quran. Then it was narrated from him that near his death he said to Ibn Naafi’, after he asked him about that, “You have irritated me. I have reflected over this matter, and there is nothing that increases except that it also decreases, and that is what is correct. And Allah, Glorified and Exalted be He, knows best.” [86] “Al-Muqaddimat” (1/57)

Ibn Taymiyyah said, “The other narration from him, and it is the more famous view among his companions, is the same as the rest that Imaan “increases and decreases.”” [87] “al-Fataawa” 97/506) | “Ziyaadatul-Imaan wa Nuqsaanihi wa Hukm al-Istithnaa’ feeh” – ‘Abd ar-Razzaaq al-Badr (p.277)