Sins are sometimes committed outwardly and other times they may have and inner and intellectual aspects. When a person tells a lie or backbites someone or commits such prohibitions, he is said to have committed a sin in the outside world but when he associates someone with God (commits shirk) or hides a testimony, he has committed a mental or an intellectual sin. Although mental sins have external implications, they have impacts and implications which are different from the sins themselves.
To swear at someone means to utter profanities. That is to say, it is a kind of revealing obscenity to someone through explicit words. Uttering profanities is among the sins which have an external aspect. Although it may be materialized in the mind as a foreground just as envying which, if revealed or turned into action against someone, would be a sin but if it is contained and is in the form of a mental occurrence with which even the individual is unhappy, most jurisprudents and scholars of ethics, relying on traditions such as hadith raf’a (liability tradition), have said that it is not a sin.
Before dealing in a detailed manner with the question, it is necessary to mention the following points:
1. Sins are sometimes committed outwardly and other times they may have inner and intellectual aspects. When a person tells a lie or backbites someone or commits such prohibitions, he is said to have committed a sin in the outside world but when he associates someone with God or hides a testimony, he has committed a mental or intellectual sin. Although intellectual sins have external implications, they have impacts and implications which are different from the sins themselves.
2. To swear at someone means to reveal meanness and obscenity to someone through the use of explicit profane words.
3. Uttering profanities is among the sins which have an external aspect. Although it may be materialized in the mind as a foreground just as envying which, if revealed or translated into action against someone, would be a sin but if it is contained and it in the form of a mental occurrence with which even the individual is displeased, most jurisprudents and scholars of ethics, relying on traditions such as Hadith Raf’a (liability tradition), have said that it is not a sin.
Having said the above, we will now draw your attention to the following:
First: Although uttering obscenities is considered to be a sin, there is no problem in them insofar as they are not uttered or expressed outwardly. However, maintaining such a mental and psychological trait and not doing away with it are undesirable as they may be materialized in the form of a sin and may also possibly entail other sins. Definitely, such a person is different from those who have no such a psychological indisposition in terms of degree and rank of spirituality and piety. As the Quran says, “O you who believe! avoid most of suspicion, for surely suspicion in some cases is a sin”, as long as the inward suspicion has not been expressed or put into action, it is not considered to be a sin. That is because suspicion is among the mental occurrences and it is something inevitable. These mental occurrences take place due, largely, to certain contexts but one should not help or persist in furthering these occurrences. Hence, it is befitting for a believer to stay away, through practice and rehearsal, from such mental and psychological traits.
Second: It is possible that what exists in the mind might erupt and turn into name-calling and swearing. That is to say, the evil trait may lead the individual to swear at others and utter offensive words. To prevent such a thing, he should try to get rid of evil quality in his mind.
Third: The Quranic verse which says, “And whether you manifest what is in your minds or hide it, Allah will call you to account according to it,” is not in opposition with what we said earlier that an obscenity is not a sin insofar as it has not been practically uttered. That is firstly because God does not punish an individual for what occurs in his mind. Indeed, if a person decides to commit a sin and he is bent on committing it, since this is an act of the mind or heart, God will punish him for this decision and for this act of the heart. The punishment will be proportionate to the sin. Secondly, the Quranic verse points out that God holds a person responsible for the outward sins which are committed through the external organs but the Quran also says that God holds a person liable and accountable for the hidden and invisible sins such as polytheism (shirk) or associating someone else with God. That is because He is the Lord of the universe and is aware of our thoughts and intentions and of every minor and major, inward and outward incidents with nothing remaining out of His sight.
Fourth: In order to further clarify the importance of avoiding obscenities and profanities, we will make mention of a few sayings from the Infallibles, peace be upon them:
1. The Holy Prophet (S) said: “Entering Paradise is forbidden to everyone who utters obscenities” That is when he does not repent sincerely and genuinely. If he does repent and apologizes to the person whom he has offended and satisfies him by doing good deeds, he will be forgiven.
2. Imam Ali (A.S.) says: “A dignified individual never swears (at another person)”
3. Imam Baqir (A.s.) said: “The weapon of base people is uttering profanities” and calling bad names and “speak to people in the same way as you would like them to speak to you because God despises those who curse believers, swears at them and taunts them and He dislikes a shameless abusive person and an insisting beggar.”
 - Makarem Shirazi, Naser, Tafsir Namunah, vol.2, p. 396, Dar al-Kutub al-Islamiyah, Tehran, first edition, 1374 (1995).
 - Naraqi, Mulla Muhammad Mahdi, Jami’ al-Sa’adat, vol.1, p. 351, A’alami Publications, Beirut, fourth edition, (without date).
 - Vide: Index “Hadith Raf’a” question 10471 (site: 10359)
 - vide: Sources on Ethics and Morality such as: Jami’ al-Sa’adaat, vol.1, p. 178 – 199; Islamic Ethics (translation of Jami’ al-Sa’adaat); Shubbar, Sayyid Abdullah, Morality, (Causes of Perish), third chapter (Cursing and Swearing) and sixth chapter (Envy). This book has been translated into other languages also. Also vide jurisprudential sources such as: Faiz Kashani, Muhammad Mohsen, Mafatih al-Sharaye’, vol.2, p. 24 – 28, Ayatollah Mar’ashi Najafi Library, Qom, first edition, (date not mentioned); Najafi (author of Jawahir al-Kalam), Muhammad Hasan, Jawahir al-Kalam fir Sharh Sharaye’ al-Islam, edited and researched by Quchani, Abbas Akhundi, Ali, vol. 41, p. 52 and 53, Dar Ihya al-Turath al-Arabi, Beirut, seventh edition (date not mentioned).
 - Hujurat, 12.
 - Al-Baqara, 284.
 - Tabarsi, Fazl bin Hasan, Majma’ul Bayan, fi Tafsir al-Quran, vol.2, p. 687 and 688, Naser Khosro Publications, Tehran, third edition, 1372 (1993).
 - Vide: Tafsir Namunah, vol.2, p. 396, Tayyib, Sayyid Abdul Hussein, Atyab al-Bayan fi Tafsir Al-Quran, vol.3, pp. 88 – 89, Islam Publications, Tehran, second edition, 1376 (1997).
 - «الْجَنَّةُ حَرَامٌ عَلَى كُلِّ فَاحِشٍ أَنْ يَدْخُلَهَا» Waram bin Abi Furas, Mas’ud bin Isa, Tanbih al-Khawater wa Nuzhat al-Nawazer better known as Warram Collection, vol.1, p. 110, Fiqh Library, Qom, first edition, 1410 A.H; Payanda Abul Qasim, Nahjul Fasahah, p. 434, Dunyaye Danish, Tehran, fourth edition, 1382 (2003).
 - «ما أفحَشَ كريمٌ قَطُّ» Tamimi Amadi, Abdul Wahid bin Muhammad, Tasnif Ghurar al-Hekam wa Durar al-Kelam, p. 223, hadtih 4496, Islamic Propagations Organizations, Qom, first edition, 1366 (1987).
 - «سِلاحُ اللِّئامِ قَبيحُ الكلام» Allamah Majlisi, Behar al-Anwar, vol.75, p. 185, Dar Ihya al-Turath al-Arabi, Beirut, second edition, 1403 A.H.
 - « قُولُوا لِلنَّاسِ أَحْسَنَ مَا تُحِبُّونَ أَنْ يُقَالَ لَكُمْ فَإِنَّ اللَّهَ يُبْغِضُ اللَّعَّانَ السَّبَّابَ الطَّعَّانَ عَلَى الْمُؤْمِنِينَ الْفَاحِشَ الْمُتَفَحِّشَ السَّائِلَ الْمُلْحِفَ وَ يُحِبُّ الْحَلِيمَ الْعَفِيفَ الْمُتَعَفِّفَ» Behar al-Anwar, vol.65, p. 152.