The Quran

108

وَلا تَسُبُّوا الَّذينَ يَدعونَ مِن دونِ اللَّهِ فَيَسُبُّوا اللَّهَ عَدوًا بِغَيرِ عِلمٍ ۗ كَذٰلِكَ زَيَّنّا لِكُلِّ أُمَّةٍ عَمَلَهُم ثُمَّ إِلىٰ رَبِّهِم مَرجِعُهُم فَيُنَبِّئُهُم بِما كانوا يَعمَلونَ

Muhammad Asad

But do not revile those [beings] whom they invoke instead of God,¹ lest they revile God out of spite, and in ignorance: for, goodly indeed have We made their own doings appear unto every community² In time, [however,] unto their Sustainer they must return: and then He will make them [truly] understand all that they were doing.

This prohibition of reviling anything that other people hold sacred - even in contravention of the principle of God's oneness - is expressed in the plural and is, therefore, addressed to all believers. Thus, while Muslims are expected to argue against the false beliefs of others, they are not allowed to abuse the objects of those beliefs and to hurt thereby the feelings of their erring fellow-men.
Lit., "thus goodly have We made...", etc., implying that it is in the nature of man to regard the beliefs which have been implanted in him from childhood, and which he now shares with his social environment, as the only true and possible ones - with the result that a polemic against those beliefs often tends to provoke a hostile psychological reaction.