In Islands in the Sea (published in Departures) by Harry Turtledove, the Muslim invasion of Constantinople succeeds in 715 and southern Europe is conquered by Muslims 700 earlier than in OTL. In the story the Muslims and Christians are trying to convince the king of Bulgars to convert to their respective religions. In the end Muslims win the argument.
I very much enjoyed this story, and I am myself interested in an academic sense in how Islam is represented in SF, In regard to ‘Islands in The Sea’ what I found most charming about the story was that, because of their representations to the King of the Bulgars, the Christian and Muslim leaders of the delegation realised that they had far more in common than they had differences. Ultimately, however, the important point is that the King makes his decision based upon very practical – rather than religious – reasons, based on who had the larger army at his borders.