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.’ [Cf. Gen. 16.8. Sozomen also says that they were descended from Agar, but called themselves descendants of Sara to hide their servile origin (Ecclesiastical History 6.38, PG 67.1412AB).] These used to be idolaters and worshiped the morning star and Aphrodite, whom in their own language they called Khabár, which means great. [The Arabic kabirun means ‘great,’ whether in size or in dignity. Herodotus mentions the Arabian cult of the ‘Heavenly Aphrodite’ but says that the Arabs called her Alilat (Herodotus 1.131)] 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, [This may be the Nestorian monk Bahira (George or Sergius) who met the boy Mohammed at Bostra in Syria and claimed to recognize in him the sign of a prophet.] 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. . . .
They furthermore accuse us of being idolaters, because we venerate the cross, which they abominate. And we answer them: ‘How is it, then, that you rub yourselves against a stone in your Ka’ba [The Ka’ba, called ‘The House of God,’ is supposed to have been built by Abraham with the help of Ismael. It occupies the most sacred spot in the Mosque of Mecca. Incorporated in its wall is the stone here referred to, the famous Black Stone, which is obviously a relic of the idolatry of the pre-Islam Arabs.] and kiss and embrace it?’ Then some of them say that Abraham had relations with Agar upon it, but others say that he tied the camel to it, when he was going to sacrifice Isaac. And we answer them: ‘Since Scripture says that the mountain was wooded and had trees from which Abraham cut wood for the holocaust and laid it upon Isaac, [Gen. 22.6.] and then he left the asses behind with the two young men, why talk nonsense? For in that place neither is it thick with trees nor is there passage for asses.’ And they are embarrassed, but they still assert that the stone is Abraham’s. Then we say: ‘Let it be Abraham’s, as you so foolishly say. Then, just because Abraham had relations with a woman on it or tied a camel to it, you are not ashamed to kiss it, yet you blame us for venerating the cross of Christ by which the power of the demons and the deceit of the Devil was destroyed.’ This stone that they talk about is a head of that Aphrodite whom they used to worship and whom they called Khabár. Even to the present day, traces of the carving are visible on it to careful observers.
Read it all at the link above.