I'm not going to check all of them, but the one from Gibbon can be found on page 890 of his Decline and Fall.

Little hint, if you put the quotations inside of quotation marks in Google like this, the search engine will return only pages with that exact quote. So for the Gibbon quote, the second result is the Google Books digitization of Decline and Fall, and the link goes directly to that page with the text highlighted.

Keep in mind that these quotes, if they are all accurate, need to be read in their original context. Taking a single statement from someone like Gibbon, Ghandi, or Napoleon and using that to make a claim about their position on Islam is, shall we say, not proper procedure.