السلام عليكم و رحمة الله و بركاتهHow many times is it must to remind someone that what they are doing is haram? Is once enough?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad, sallallaahu ʻalayhi wa sallam, is His Slave and Messenger.

It is not sufficient to forbid the sinner who is persistently committing a prohibited act once. We have previously underlined in our Arabic Fatwas that forbidding the evil is not confined to a specific number of times. A Muslim is required to forbid sinful acts whenever they recur to the best of his ability and as long as his advice would hopefully be effective. When a Muslim sees someone committing a sinful act, he should forbid this person kindly and wisely; if he happened to see him again committing a sinful act, he should forbid him again and so on.

Whenever he sees this sinner committing a sinful act, he should forbid him even if he believes that such a sinner would most likely reject his advice so that he would be absolved before his Lord and hoping that the advised person would listen and refrain from committing that sinful act. Allah, The Exalted, says (what means): {And when a community among them said, "Why do you advise (or warn) a people whom Allah is (about) to destroy or to punish with a severe punishment?" they (the advisors) said, "To be absolved before your Lord and perhaps they may fear Him."} [Quran 7:146]

Those who forbade the sinners from their sin keenly continued to forbid them and remind them of the need to abide by the commands of their Lord and evade His prohibitions. Another group of the obedient people thought that there was no point of advising those persistent sinners and forbidding them from their disobedience. The verses underline that those who continued to forbid the persistent sinners from committing such a sinful act had two objectives:

First, they wanted to be absolved before their Lord so that they would not be neglectful of the obligation of forbidding the evil. Allah, The Exalted, has enjoined those endowed with the knowledge to teach others and never to despair due to their slow response and acceptance of their advice.

Second, the advised people would ultimately listen to them and act upon their advice; many sinners repent to Allah after being advised.

Al-Haafith Ibn Rajab wrote, "Al-Qaadhi Abu Yaʻli related two opinions for Imam Ahmad regarding the obligation of forbidding an evil when it is known that the advised person shall not accept the advice. He held that the most likely correct view in this regard is that it is incumbent to forbid the sinner in this situation and this is the opinion of most scholars. Some of the righteous predecessors remarked that such an act is hoped to be a reason to be absolved before Allah. Allah, The Exalted, has informed us about the people of As-Sabt in the Quran and how a group of the obedient people kept advising and forbidding those persistent sinners and said as related in the verse that reads (what means): {"Why do you advise (or warn) a people whom Allah is (about) to destroy or to punish with a severe punishment?" they (the advisors) said, "To be absolved before your Lord and perhaps they may fear Him."} [Quran 7:146]" [Sharh Al-Arbʻeen An-Nawawiyyah]

What further proves that forbidding the evil is not confined to a specific number of times is the general indication of the following Hadeeth. The Prophet, sallallahu ʻalayhi wa sallam, said: “Whoever among you sees an evil action and can change it with his hand (by taking action), let him change it with his hand. If he cannot do that, then with his tongue (by speaking out); and if he cannot do that, then with his heart (by hating it and feeling that it is wrong), and that is the weakest of faith.” [Muslim]

An-Nawawi wrote in his commentary on Saheeh Muslim, “If a Muslim, who is competent for religious assignments, believes that his advice would not be effective, the obligation of enjoining the good and forbidding the evil is not waived. He is still legislatively required to observe this religious obligation; verily, the reminder benefits the believers. We have previously underlined that he is merely required to enjoin the good and forbid the evil and he is not responsible for the acceptance of his advice.”

ʻAbdullaah ibn Masʻood narrated that the Prophet, sallallaahu ʻalayhi wa sallam, said: “The first defect that permeated the Children of Israel was that a man (of them) met another man and said, 'O so-and-so, fear Allah, and abandon what you are doing, for it is not lawful for you. He then met him the next day and that did not prevent him from eating with him, drinking with him and sitting with him. When they did so. Allah mingled their hearts with each other.” He, sallallaahu ʻalayhi wa sallam, then recited the verse that reads (what means): {Cursed were those who disbelieved among the Children of Israel by the tongue of David and of Jesus, the son of Mary ... are defiantly disobedient.} [Quran 5: 78-81] The Prophet, sallallaahu ʻalayhi wa sallam, then added: “Nay, by Allah, you must enjoin what is good and prohibit what is evil, prevent the wrongdoer, bend him into conformity with what is right, and restrict him to what is right.” [Abu Daawood]

Allah knows best.