Cursing or Insulting the god of other religions is strictly forbidden under Islamic law as stated in the Qur’an: “And do not insult those they invoke other than Allah, lest they insult Allah in enmity without knowledge. Thus, We have made pleasing to every community their deeds. Then to their Lord is their return, and He will inform them about what they used to do. “[Al-An’aam (6): 108]
Based on the verse, Muslims are strictly forbidden from cursing or insulting the gods of non-Muslims. If Muslims do, they may curse or insult Allah back to defend their god, even though they have absolutely no correct and fair knowledge of Allah. Therefore, Muslims should prevent other Muslims from cursing or insulting the God of other religions so that there is nothing cursing or insulting each other.
Once again, under Islamic law, the act of cursing or insulting the god of other religions cannot be accepted in any manner and for any purpose whatsoever, and no matter what the situation is. Whether it’s just joking or serious, whether it’s in an open or closed forum, or even in a preaching situation in mosques, it still cannot be accepted. Who can be sure of the curses or insults to their god will not spread and reach their ears? If it comes to pass that they hear the words of the insults, they would, of course, defend their god. It would likely mean cursing or insulting Allah back. It also means the Muslims cursing or insulting their god may, would make Allah being cursed or insulted. This is a sin before Allah.
If Muslims find their fellow Muslims whose inappropriate words by cursing or insulting the god of other religions, they should warn them not to do what they did. It does not matter whether the persons whose inappropriate words are ordinary Muslims or clerics, the persons have to be seriously warned. It is hard indeed, to make people aware of their mistake due to many factors inside. One of them is pride. They are may aware of their serious mistake, and yet their self-assurance makes them refuse to accept they have made a mistake.
Let alone ordinary Muslims, even clerics can make such serious mistakes, because basically they are merely humans. Who did not make mistake sometimes? Only God does not make mistakes humans do. It is obligatory for Muslims to warn them. Muslims should not even participate in supporting of such forbidden actions just for solidarity reasons as fellow Muslims. Moreover, for those who are warned, they have to aware of their serious mistake, and accept it.
A careful cleric, then he will deliver preaching in a way that does not violate the prohibition of Allah. A positive preaching will touch the heart of people and transmit peace to others. Conversely, a provocative preaching, by insulting other religions and their god, can cause hatred, anger, and enmity among religious faiths, and also religious sentiments. Such provocative preaching is one root of the intolerance. Preaching is to spread the doctrines of Islam peacefully, so that the preacher has to limit topics on matters of Islam alone.
Allah Almighty says: “Say, “O disbelievers, I do not worship what you worship. Nor are you worshippers of what I worship. Nor will I be a worshipper of what you worship. Nor will you be worshippers of what I worship. For you is your religion, and for me is my religion.” [Al-Kaafiroon (109): 1 – 6]
Prophet Muhammad (pbuh) is the role model for all Muslims. He delivered the teachings and doctrines of Islam leniently. In his time, preaching was delivered peacefully. There were no a provocative speech and incitement to hatred of other religions because there is indeed no compulsion in the religion of Islam. In his time, Muslims could coexist with other religious believers and with non-believers in peace.
Allah Almighty says: “There shall be no compulsion in (acceptance of) the religion. The right course has become clear from the wrong. So whoever disbelieves in Taghut and believes in Allah has grasped the most trustworthy handhold with no break in it. And Allah is Hearing and Knowing.” [Al-Baqara (2): 256]
“So by mercy from Allah, [O Muhammad], you were lenient with them. And if you had been rude [in speech] and harsh in heart, they would have disbanded from about you. So pardon them and ask forgiveness for them and consult them in the matter. And when you have decided, then rely upon Allah. Indeed, Allah loves those who rely [upon Him].” [Aal-i-Imraan (3): 159)]