The wisdom of St. John of Damascus
Below is given the the testimony of St. John of Damascus and his comments on what he knew to be "the superstition of the Ishmaelites", and what we today call "Islam". It is informative to the modern reader because it shows us that many of the things that scholars are only now revealing about Islam, was in fact known about the Great Heresy all the way back in the 8th Century, just a hundred years or so after the spread of the early form of that perversion of the Word.
There is also the superstition of the Ishmaelites which to this day prevails and keeps people in error, being a forerunner of the Antichrist. They are descended from Ishmael, [who] was born to Abraham of Agar, and for this reason they are called both Agarenes and Ishmaelites. They are also called Saracens, which is derived from Sarras kenoi, or destitute of Sara, because of what Agar said to the angel: ‘Sara hath sent me away destitute.’  These used to be idolaters and worshiped the morning star and Aphrodite, whom in their own language they called Khabár, which means great.  And so down to the time of Heraclius they were very great idolaters. From that time to the present a false prophet named Mohammed has appeared in their midst. This man, after having chanced upon the Old and New Testaments and likewise, it seems, having conversed with an Arian monk,  devised his own heresy. Then, having insinuated himself into the good graces of the people by a show of seeming piety, he gave out that a certain book had been sent down to him from heaven. He had set down some ridiculous compositions in this book of his and he gave it to them as an object of veneration.