In his famous commentary of Sahih Muslim, Imam al-Nawawi includes a section entitled Forbidding what is Wrong is Part of Iman. The following is an excerpt:

The Prophet ﷺ said that whoever sees a wrongful action he ‘should change it’. This is a compulsory order according to unanimous understanding. That enjoining what is right and forbidding what is wrong are duties is endorsed by the Qur’an, the Sunnah and the unanimous verdict of the Muslim community. Furthermore, it is an aspect of sincere counselling, which is the essence of the Islamic religion.

The only people who dissent from this view are a minority of Shia, and their disagreement is not taken into account. Imam al-Haramayn [al-Juwayni] said: ‘Their disagreement is discounted, because the Muslim community were unanimous on this before such people came into existence. That this is a duty is determined by Islam, not by reason as the Mu‘tazilah claim. A Qur’anic verse says: ‘Believers, it is but for your own souls that you are accountable. Those who go astray can do you no harm if you [yourselves] are on the right path’. (5:105)

This is not contrary to what we have just said. According to most scrupulous scholars, the verse means that when you have done your duties, then the failure of others to do their duties will not cause you any harm. This is the same as the Qur’anic principle: ‘No soul will bear the burden of another’. (35:18) As it is so, then one of the duties of every Muslim is to enjoin what is right and forbid what is wrong. If one does so but the addressee pays not heed, no blame attaches to the one who has done it because he has discharged his duty, which is to enjoin and forbid, without ensuring acceptance. It is Allah who knows best.

Besides, enjoining right and forbidding wrong is a collective duty: when some people do it, the others are exempt, but if all people ignore it, every one of them who is able to do so, with neither excuse for failure nor fear, incurs a sin. Moreover, it may become a personal duty, when someone is the only person who is aware of the wrongful action, or the only one who can change it. This is the case of someone who sees his wife, or child, or servant doing some wrong or failing to do what is right.  Scholars say that a person is not exempt from enjoining right and forbidding wrong because he believes that it will be useless. Even in this case the duty is binding, because reminders benefit believers. As we have already stated, his duty is to give the advice, but he is not responsible for its acceptance. It is as Allah says: ‘The Messenger’s duty is but to deliver the message [entrusted to him]’ (5:99). Scholars cite the example of a person in a public bath or a swimming pool who sees someone with an area of his body that must be covered being uncovered; but Allah knows best.

Scholars say that it is not a condition that the one who enjoins what is right and forbids what is wrong should himself be in a perfect state, doing what he enjoins others to do and refraining from what he forbids them. He should do so, even though he fails to do what he enjoins or does what he forbids. The point here is that he has two duties: to give such instructions to himself and to give the same instructions to others. If he fails to do one of these two duties, does such failure make it permissible to fail in the other duty?

Scholars add that enjoining right and forbidding wrong is not incumbent only on those who are in authority. It is applicable to all Muslim individuals. Imam al-Haramayn said: ‘The evidence in support of this is the unanimity of the Muslim community. In the early period of Islam and the following generations, ordinary people used to enjoin governors and people in authority to do what is right and  voice their disapproval of any wrong they may do.’ The Muslim community approved their deeds and none was criticized for so doing even though they held no position of authority, but Allah knows best.

Moreover, a person must know what he is enjoining or forbidding and this differs according to the matter in question. If it is one of the obvious duties or the well-known prohibitions, such as prayer and fasting or adultery and drinking, all Muslims are aware of these*. If it is a question of subtle details or something that is subject to scholarly discretion, i.e. ijtihad, lay people cannot address such matters and they may not speak about them. It is left to scholars who should express their criticism only on what is unanimously agreed. If something is controversial, they may not speak against it. According to one view, every scholar who exercises discretion, or ijtihad, is correct. This is the view chosen by the majority of scrupulous scholars. The other view is that only one is correct, while the incorrect one is unknown to us. No sin attaches in this case. However, if it is done by way of advice so as to avoid controversy, then it is perfectly appropriate, provided it is done gently. Scholars agree that steering away from what is subject to disagreement is to be encouraged, provided that it does not lead to neglecting a Sunnah or involves another type of disagreement.

…

It must be known that this aspect of Islam, i.e. the enjoining of what is right and forbidding of what is wrong, has largely been neglected for a very long time and very few aspects of it remain. Yet it is very important, indeed it is the principle that ensures society remains on the right course. When evil spreads, punishment is inflicted on the good and the bad alike. Unless people stop injustice, Allah may well extend his punishment to all of them. He says: ‘Let those who would go against His bidding beware, lest some affliction or painful suffering befall them’ (24:63). Its benefit is great indeed, particularly because it has been largely neglected, and a person who seeks success in the life to come and hopes to earn Allah’s pleasure should be keen to undertake this duty. He should be sure of the sincerity of his intention and fear no one, regardless of his authority. Allah says: ‘Allah will most certainly succour him who succour’s Allah’s cause’; (22:40) ‘He who holds fast to Allah has already been guided along a straight path’; (3:101) ‘As for those who strive hard in Our cause, We shall most certainly guide them to paths that lead unto Us’; (29:69) ‘Do people think that once they say: “we are believers”, they will be left alone and will not be put to a test? We certainly tested those who lived before them; and so most certainly Allah knows those who speak the truth and most certainly He knows those who are liars’ (29:2-3).

Everyone should now that Allah’s reward is commensurate with the effort exerted for His sake. A person should not refrain from undertaking this duty because of his friendship with the person to be advised or in order to please him or to gain favour with him, or to ensure that he retains his position with him. The fact that he is a friend indicates, by virtue of that friendship, a right due to him, which is to be given sincere advice and to be shown the way that enhances his position in the life to come or spares him an adverse effect there. A true friend, who sincerely loves his friend, tries to improve his position in the life to come, even if this involves some loss in this life. A person’s enemy is one who leads him to a loss in the Hereafter, even though it brings him some advantage in this life. Satan is our enemy because of this, while all prophets were friends and protectors of believers because they guided them to what improves their position in the life to come. We pray to Allah to guide us and our loved ones and all Muslims to what pleases Him and to bestow His generosity and mercy on us all.

A person who enjoins what is right and forbids what is wrong should be gentle in his approach, so that he is better able to achieve his purpose. Imam al-Shafi‘i said: ‘Whoever admonishes his brother in private give him advice in a respectful manner, but the one who admonishes his brother in public exposes his failure and puts him to shame’. In this connection, people often turn a blind eye when they see someone selling another a faulty article without mentioning the fault. They neither declare their disapproval of this practice, nor inform the buyer of the fault in the article to be purchased. This is clearly wrong and scholars declare that whoever is aware of any such fault should make his disapproval clear to the seller and inform the buyer, and Allah knows best.

The prohibition of what is wrong should be exercised and its degrees have been outlined by the Prophet ﷺ, as he said: ‘Whoever of you sees a wrongful action should change it with his hand; and if he is unable to do so, then with his tongue; and if he is unable to do that, then with his heart’. That the Prophet ﷺ said, ‘then with his heart’, means that a person should mentally dislike the wrong action, even if he cannot do anything about it. This does not mean that he actually changes it, but he does what he can. The Prophet ﷺ describes this last attitude as ‘the weakest degree of faith’. This means that it yields the least result, but Allah knows best.

Al-Qadi al-‘Iyad said: ‘This hadith gives us a clear statement of how change should be affected. The one who undertakes such a change should resort to everything he can in order to achieve his purpose, whether by word or deed. He may break the tools used to do what is wrong, or pour an intoxicant drink down the drain, or return to the rightful owners what was wrongfully taken away from them, doing any of these himself or giving orders for it to be done. When a person undertakes such a change, he should be gentle with the one who is ignorant of the perpetrated wrong, and with the one who is in a strong position to cause harm. A gentle approach is more likely to make his advice acceptable. It is also recommended that the one who undertakes such a change should be known as a God-fearing and pious person. He may rebuke the one who is persistent with wrongdoing if he feels that such a rebuke would not lead to an even worse evil than the one he is changing. If he thinks that a physical change could lead to a worse evil, such as endangering his own life or the life of someone else, then he should refrain from physical change and resort to verbal advice, reminding the person concerned of the consequences of his wrongful action. If he again fears that such admonition may bring about bad results, then he should stop at mental disapproval. This is the message given in this hadith. However, if the one who wants to change a wrongful action is able to find support for his purpose, he should call on this support, unless this leads to the use of arms and to a fight. He may also put the matter to the relevant authorities, or limit himself to mental disapproval. This is the right understanding of this issue and how it should be implemented, as suggested by eminent and scrupulous scholars. This is contrary to the view that requires speaking out against wrongful action in all situations, even if it causes physical injury or the death of the person who so speaks.’

Imam al-Haramayn said: ‘It is perfectly permissible for any citizen to physically prevent a person who intends to commit a major sin, if he will not take heed of verbal advice. This is so, provided that the matter does not end in a fight and drawing arms. If it becomes so, the matter should be referred to the authorities. If  a ruler enforces measure of injustice and this becomes clear and he does not pay heed to advice but persists in wrongdoing, it is permissible for the leading figures in the community to collaborate to remove him even if this requires the drawing of arms and a fight.’ What Imam al-Haramayn suggests is strange indeed, but it is understood to be conditional on being sure that it would not lead to a worse situation. Imam al-Haramayn further adds: ‘It is not open to the one who undertakes enjoining right and forbidding wrong to search or spy on people, or force his way into homes on suspecting the commitment of wrongful action. Only when he sees or finds something wrong does he change it’.

[Sahih Muslim With the Full Commentary by Imam al-Nawawi, volume 2, translated and edited by Adil Salahi, Islamic Foundation, Markfield, 2019, pp. 6-12]

*Another category that could be added here is those matters upon which there is agreement among the Imams of the four Sunni schools of law, such as the necessity of having a Caliph/Imam. Qadi Safadi writes: “The Imams [Abu Hanīfah, Al-Shafi‘i, Malik and Ahmad bin Hanbal] agree that having a ruler [Caliph] is an obligation and that the Muslims must have a ruler to establish the practices of the dīn and to give justice to the wronged from those who have wronged them…” See here for the full quote.

NB

There needs to be a clarification here of whether it is permitted to remove the ruler in certain circumstances.

Al-Bukhari narrated on the authority of Junada bin Abi Umayyah who said: “We went to ‘Ubadah bin as-Samit when he was sick and we said: May Allah guide you. Inform us of a Hadith from the Messenger of Allah ﷺ so Allah may benefit you from it. He said: “The Messenger of Allah ﷺ called upon us and we gave him the bay‘ah (pledge of allegiance), and he said, of that which he had taken from us, that we should give him the pledge to listen and obey, in what we like and dislike, in our hardship and ease, and that we should not dispute the authority of its people unless we saw Kufr buwah (clear and explicit disbelief) upon which we had a proof from Allah.”

Dr. Muhammad Khair Haikal states in his Al-Jihad Wal-Qital fi as-Siyasah ash-Shar‘iyyah [English translation] the following:

‘As for what is related to al-Kufr al-Buwah (clear and explicit disbelief) and what relates to that, the following was mentioned in al-Nawawi’s commentary of Sahih Muslim:

“Al-Qadi al-‘Iyad said: ‘The ‘Ulama have held a consensus (Ijma‘) that the Imamah is not contracted to the Kafir and that if (after) al-Kufr (disbelief) occurs from him, he is deposed.’ He said: ‘The same applies if he abandons the establishment of the Salah and the call to it.’ ”

He then says: “Al-Qadi [al-‘Iyad] said: ‘So if he is overtaken by Kufr or by a changing of the Shar‘a (divine legislation) or by a bid‘ah (innovation) he exits from the Hukm of the Wilayah (the position and responsibility of ruling). Obedience to him no longer stands and it is obligatory for the Muslims to rise and stand against him, remove him and appoint a just (‘adil) Imam, if that is possible.” ’

[Haikal, op. cit., p. 189 quoting al-Nawawi’s commentary of Sahih Muslim, 8/35-36]