In Bangladesh, it is a common habit amongst non-practising Muslims (as well as non-Muslims) to insult with the term 'shala' (which means, 'my wife's younger brother', even if the person called shala is not his wife's brother). Is that permissible?
All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah and that Muhammad is His slave and Messenger.
If this word is used as an insult in your country, then it is impermissible to use it to ridicule or insult your fellow Muslims.
Allaah, The Exalted, forbade the believers from verbally abusing one another. It is a general prohibition including all the names and titles that a Muslim dislikes to be called with. Allaah, The Exalted, says (what means): {Wretched is the name of disobedience after (one's) faith.} [Quran 49:11] Ibn Katheer commented on the verse saying, "It is wretched that you call each other with (evil) names like the people of the pre-Islamic era used to do after you have embraced Islam and understood it."
It is also impermissible to use this word to insult or mock a non-Muslim who is not at war with the Muslims. The Kuwaiti Encyclopedia of Fiqh reads:
"When a Muslim insults or verbally abuses a Thimmi (non-Muslim living under the protection of the Muslim state), he has committed an evil deed; the Muslim should be subject to taʻzeer (discretionary punishment) for insulting or cursing a non-Muslim. The Shaafiʻis held that the Muslim should be subject to taʻzeer for insulting or cursing a non-Muslim regardless of whether he is alive or dead and known to have died as a disbeliever. The Hanbali scholar Al-Buhooti said, 'Taʻzeer is prosecuted here to fulfill the right of Allaah.'"
As for the mafhoom (the understood meaning which is not explicitly stated) in the hadeeth in which the Prophet said, "Cursing a Muslim is an immoral act." [Al-Bukhari and Muslim], As-Sanʻaani wrote, "The mafhoom in this hadeeth indicates that it is permissible for the Muslim to curse a non-Muslim. However, if this non-Muslim is mu'aahad (i.e. protected by virtue of a peace treaty with Muslims), then this action constitutes harm inflicted upon him, which is deemed prohibited. Hence, the indication of the mafhoom in this hadeeth is not acted upon in case of the mu'aahad. However, if the non-Muslim is a combatant (fighting against Muslims), then it is permissible to curse him because he has no protection under the sharee'ah..." [Subul As-Salaam]
The Muslim is enjoined to guard his tongue against immoral or vulgar language in general. The Prophet said, "Indeed, the believer is not a slanderer, nor a cursor, nor a vulgar outrageous person." [At-Tirmithi and Ahmad - Al-Albaani graded it saheeh (sound)]
Allaah knows best.
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