It is natural for Muslims to believe that there is a "Plural of Respect" in the Bible. That's like the "Royal we", as in the well-known phrase "We are not amused", where it is just the queen speaking.
Muslims readily believe this is because, in the Quran, Allah likes to refer to himself in the plural for some reason.
I have seen this come up when talking to Muslims in these two situations:
Explaining the Trinity from the Old Testament ("Let us create man in our image").
Mohammed in the Song of Solomon 5:16 ("Muhammedim"), part of the attempt to show that Muhammed is in the Bible.
The response is that this "plural of respect" does not exist in the Old Testament, in the sense that you do not see any kings (or anyone else) refer to themselves in the plural form.
Also this way of addressing God, or anyone, in the plural, is never found in the New Testament.
