Most places of worship don't allow people coming in to carry a firearm. So even if someone wanted to have a gun in the mosque, it was probably against the organization's policy. Even here in the US, you only recently could legally carry a firearm into a house of worship.
Plus, I'm not sure how many people get up and head off to worship services and think they need to be armed. A vast majority of people practicing Islam are incredibly peaceful people. I can't see many of them owning firearms to begin with anyway since it goes against their peace message.
Also, it's a little odd you want to tuck that away for future reference, are you planning on robbing him or something? I'm not sure why you'd ever need to know if someone was armed or not unless you plan on violating their rights in some way and, you know, don't want to get shot.