You have made the app for special users, which means there are less users than normal apps. However, your app also will get less competition. In order to attract more Muslims to install your app, you need:
-Keyword optimization (Find the relevant, competitive and most searched keywords; Spy on your competitors' app name, keywords and description; rely on app reviews)
- Buy installs from some special providers. This method will rank app top with targeted keywords and will drive more new users.
-Gain positive reviews from real users.
Hope this will be helpful for you.
Wish you luck!