Introduction
The concept of the conjunction between the outward and the inward states
This means that there is a link between the apparent state and the inner state, and there is an impact of each on the other, wherein it is impossible to envisage the presence of true faith in the inner self without its requirement and demand being manifest in the deeds of the limbs in both verbal and practical forms. Rather, where faith is found in the interior, it is necessary for the body to activate the possible actions of the limbs. The outward action is necessary for the inner faith that cannot be separated from it, and the negation of the imperative is evidence for the negation of what it is obliged for. Thus, from the total absence of the apparent deeds, the corruption of the inner self can be inferred.
Ibn Taymiyyah states, “If the heart establishes belief in it and love for it, it is necessary for the body to move according to that in terms of the apparent words and outward actions. What appears on the body in terms of words and actions is the cause and necessity of what is in the heart, and its evidence and its effect, just as what the body does in words and actions also has an effect on what is in the heart, so each of them affects the other. However, the heart is the root, and the body is a branch to it, and the branch derives from its root, while the root is established and strengthened by its branch.” [765] Majmoo’ Al-Fataawaa, (7/541).
Evidence of the correlation between the outward and the inward states
1- The saying of Allah Almighty, “And if they had believed in Allah and the Prophet and what was sent down to him, they would not have taken them as sincere allies.” Al-Maa’idah: 81.
Faith inwardly entails enmity with the unbelievers and abandoning allegiance to them outwardly.
Ibn Jareer said, “The Almighty says: if those who befriended those who disbelieve, from amongst the children of Israel “believed in Allah and the Prophet;” He thereby says, “If they affirmed in Allah and acknowledged him and took Him as One God and affirmed in His Prophet Muhammad ?, meaning that he is a sent Prophet and a sent Messenger,” “and believed in what was revealed to him;” He thereby says, “Affirmed in what was revealed to Muhammad ? from Allah of the ayaat of Criterion. “Then they would not take them as sincere allies;” He says thereby, “Then they would not take them as companions and helpers besides the believers. “However, many of them are disobedient;” He thereby means, “However, most of them are a people who have exited from the obedience to Allah by going towards His disobedience, and a people who make what Allah has forbidden them permissible in terms of saying and doing.”” [766] Tafseer of Ibn Jareer, (8/593).
2-   The words of Allah Almighty, “You will not find those who believe in Allah and in the Hereafter having friendship with those who oppose Allah and His Messenger, even though they may be their fathers or their sons or their brothers or their clan. They are such that Allah has inscribed faith on their hearts and has supported them with a spirit from Him. He will admit them to gardens beneath which rivers flow, in which they will live forever. Allah is pleased with them, and they are pleased with Allah. Those are the party of Allah. Be assured that it is (the members of) the party of Allah that are the successful.”  Al-Mujaadalah: 22.
Ibn Taymiyyah said, “Since the outward words and actions were a necessary part of and necessitated by the inner sayings and actions, the former was inferred from the latter, as found in the Almighty’s saying, “You will not find those who believe in Allah and in the Hereafter having friendship with those who oppose Allah and His Messenger, even though they may be their fathers or their sons or their brothers or their clan. They are such that Allah has inscribed faith on their hearts and has supported them with a spirit from Him.” Al-Mujaadalah: 22.  Allah informed that those who are believers in Allah and the Last day are not found to be liking the enemies of Allah and His Messenger, rather the same faith is contrary to their liking. If liking is found, then that indicates the defect of faith, as well as Allah’s saying which is indicative of that, “You see many of them take the disbelievers (the pagans) for friends. Indeed, evil is what they have sent ahead for themselves, for Allah is angry with them, and they are to remain in torment for ever. If they believed in Allah, in the prophet, and in what had been sent down to him, they would have not taken them (the pagans) for friends, but many of them are sinners.” Al-Maa’idah: 80-81 [767] Majmoo’ Al-Fataawaa, (7/542).
3- The Almighty’s statement, “Say if you love Allah, then follow me.” Aal ‘Imraan: 31.
When love/liking is established in the heart with affirmation, it is necessary for the body to move according to that in terms of the outward words and outward deeds.
Ibn al-Qayyim states, “If their love of Him signifies the reality of servitude to Him and its secret, then it only realises by following His command, and by avoiding His prohibitions. During following the command and avoiding the prohibition, the reality of servitude and love become apparent. For this reason, the Almighty made following His Messenger a sign for that, and a witness for whom he claims that love, Allah states, “Say, ‘if you love Allah, then follow me, Allah will love you.’” Aal-‘Imraan: 31 He, the Almighty, made following His Messenger contingent to their love of Allah, and a condition for Allah's love for them. The presence of contingent without the existence of its condition. Thus, the realisation of the contingent is dependent on the realisation of the condition. Thus, the absence of love became known during the inexistence of following.  Hence, the absence of their love for Allah necessitates the absence of following His Messenger, and the absence of following him is necessitated by the absence of Allah’s love for them, so it is impossible, then, to prove their love for Allah, and to prove Allah’s love for them, without following His Messenger.” [768] Madaarij as-Saalikeen, (1/119).
4. An-Nu’maan ibn Basheer said, “I heard the Messenger of Allah ? say, “Be attentive! Verily, in the body there is an organ, if it is sound then the whole body is sound, and if it is unsound, then the whole body is unsound. Listen carefully! It is the heart!”” [769] Narrated by Al-Bukhaaree (52) and the wording is his, and Muslim (1599).
Haafith Al-Hakamee says, “It is impossible for the submissiveness of the limbs to the apparent actions to be absent with the proof of the existence of the action of the heart ... . Hence, it becomes clear to you that whoever said among Ahl as-Sunnah concerning faith (Imaan): ‘It is defined as affirmation according to the apparent linguistic meaning;’ they only meant thereby the submissive affirmation that necessitates complete submission outwardly and inwardly, undoubtedly; they did not mean mere affirmation.” [770].Ma’aarij al-Qabool, (2/594).
The unanimity of Ahl As-Sunnah that action is a part in which faith is not valid without it.
Several scholars of Ahl as-Sunnah have narrated consensus concerning the fact that action is a part in which faith is not valid except with having it, and the explanation of that is as follows:
Ash-Shaafi’ee says, “The consensus of the Companions and the followers and those who came after them from those we encountered was that they stated, “Faith is a statement, an action, and an intention, and none of the three suffices except with the other.” [771] Sharh Usool ‘Itiqaad Ahl as-Sunnah, by Al-Laalkaai (5/957); Majmoo’ Al-Fataawaa, by Ibn Taymiyyah (7/209).
Al-Humaidi said, “I was told that some people say: ‘Whoever affirms prayer, Zakaat, fasting, and pilgrimage, and does not do any of that until he dies, or prays facing the opposite direction of the Qiblah until he dies; then, he is a believer as long as he does not deny ... .’   This is ironic! When recognising the obligations and facing the Qiblah correctly, yet, he does the opposite! Thus, I state, ‘This is open blasphemy, and it is contrary to the Book of Allah and the Sunnah of His Messenger ? and the action of the Muslims.” [772] Al-Khallaal in “Al-Sunnah” (3/586), and Al-Laalkaa’i in “Sharh Usool ‘Itiqaad Ahl as-Sunnah,” (5/957).
Aboo Taalib al-Makkee says, “The Ummah is unanimous that if a person believes in all the contracts of the heart that we have mentioned in the hadeeth of Jibreel (Gabriel), peace be upon him, regarding the description of faith, and does not act upon what we have mentioned in terms of the description of Islam based on the actions of the limbs, then, he cannot be called a believer. If he acts upon what has been described as part of Islam, but he fails to have in what Jibreel has described as part of faith (Imaan), then he cannot be a Muslim, and he (the prophet) ? has told that the Muslim Nation cannot not gather on misguidance.” [773] Qoot al-Quloob, (2/219).
Muhammad ibn ‘Abd al-Wahhaab says, “There is no dispute among the Ummah that monotheism must be by the heart, which is knowledge, and by the tongue, which is speech, and by action, which is the implementation of commands and prohibitions. If he violates any of this, then the man is not a Muslim. If he affirms monotheism, and does not act upon it, then he is a rebellious infidel, like Pharaoh and Satan. If he acts upon monotheism outwardly, and does not believe in it inwardly, then he is a pure hypocrite, worse than an infidel. And Allah knows best.” [774] Al-Durar Al-Sanniyyah, (2/124).
It has been mentioned in the book known as at-Tawdeeh ‘an Tawheed Al-Khallaaq, “The people of the Sunnah are unanimously agreed that when the action of the heart ceases only, or its ceasing is combined with the action of the limbs, faith ceases in its entirety, then if mere affirmation is found, it will not benefit for its being devoid of the actions of the heart and the limbs together, or of one of them, just as it did not benefit Iblis, Pharaoh and his people, and the Jews and the polytheists, who believed in the truthfulness of the Messenger secretly and openly.” [775] At-Tawdeeh ‘an Tawheed Al-Khallaaq, (p.: 139) and the book was printed and attributed to Shaykh Sulaymaan bin Abdullah bin Muhammad bin ‘Ad al-Wahhaab, while Abdul Azeez bin Muhammad Al Abd Al-Lateef verified its attribution to three Imaams of the Da’wah who participated in it, and they are: Muhammad bin ‘Alee bin Ghareeb (died: 1209 AH), Hamd bin Mua’mmar (died: 1225 AH), and Abdullah bin Muhammad bin ‘Ad al-Wahhaab (died: 1242 AH). See: Da’aawaa al-Munaawi’een, (p.: 59).