This is "Stephanus" of Alexandria, who probably was from that city, as translated by Robert Hoyland p. 304. First Stephen cites one Epiphanius, an Arab merchant,
who has just returned from "Arabia Felix" and hastens to
Stephen's place of teaching in order to inform him of the "new"
and "strange" events taking place in that country:
In the desert of Ethrib there had appeared a certain
man from the so-called tribe of Quraysh (Korasianov),
of the genealogy of Ishmael, whose name was Muhammad
and who said he was a prophet. He appeared
in the month of Pharmuti, which is called April by
the Romans, of the 932nd year (from the beginning of
Philip). He has brought a new expression and a strange
teaching, promising to those who accept him victories
in wars, domination over enemies and delights in paradise.
More text exists in English, translated and annotated by Otto Neugebauer and H. B. Van Hoesen. I have extracted this excerpt hence. I'm on L621 which is 158f, which they translated from Usener 273-5.
The aforesaid merchant came to
us in the month Thoth, according to the Egyptians.
(5, day 3, hour 3).2 And we find the sun occupying
9:5 in Virgo. Referring this to the astrolabe we found
(for the)3 3rd hour of day that the 20th degree of Libra
was rising and the 22d degree of Cancer in Midheaven.
Similarly the 20th degree of Aries was setting and in
Lower Midheaven was the 22d degree of Capricorn. Oh the misery! alas the change of things! Libra is
rising, (being) the exaltation and day-triangle4 of
Saturn; Saturn itself being in Midheaven, approximately
in the very degree of Midheaven and in the terms of
Venus,5 and Venus itself in Agathodaemon,6 together
with the ascending node, and in the sign of Leo. The
horoscopic premise then indicates a nation of Saturnian
type and a state akin to Venus, rising quickly and
mastering many nations; for rising Libra7 brings servitude to all men. Further, Saturn being actually in the
South and Venus likewise in the South8 indicate a
nation from the South, outstanding in great strength and
unrestrained speed and constant motion and of enduring
possession, with epic battles and most brilliant deeds of
valor and distinguished by a new type of state. And
further, because Saturn was high in Midheaven this
(nation) has an unrestrained spirit and irrepressible
enterprise. And it opposes the nations (belonging to)
Jupiter and Mars until it comes to the dominion of the sun; for only the nations (belonging to) the sun are exempt from the yoke of such a nation [etc., making, e.g., Venus responsible for observing the sixth day in Islam.]. It prevails over all Egypt and Libya — Egypt as belonging to Mercury and Libya to Mars — and also Palestine and Syria as belonging to the moon and Mercury. It drives the Roman nation from all Syria and the other countries, and subdues, slaughters, and imprisons Cilicia; and it will completely devastate Cappadocia, because of Mars. But it will not overwhelm the kingdom of the Romans itself, because of the sun and because of Mars being near Midheaven. And further, because of Mars being in its own depression, that is in Cancer, the nations belonging to Mars will be in depression in the face of this people: but because of Mars itself being in Midheaven. the kingdom of those people under it (Mars) will remain, that is the (kingdom) of the Romans and the Turks and the Khazars and the Bulgars and the like.9 Further also because of Jupiter being in his own depression, namely in Capricorn, the kingdom of the eastern peoples and of the Persians themselves will be entirely suppressed by this nation [etc.]. And all Persia will be subjugated as far as the Indians; and further, because of Jupiter in his own depression and in Lower Midheaven, Armenia and Iberia and Colchis and parts of Scythia, because of Mars.
Sadly neither of these translate as far as what they had of Islamic history past that. And Neugebauer's and Van Hoesen notes are mainly for astrologers - actual students, not believers in it or those who prey upon them. There are a couple comments worth raising there though.
#7 points out that the Roman Libra "scale" is actually the Greek yoke, so this is a pun. #9 notes that the Islamic empire had reached this extent, but had not conquered Constantinople, as of ('Umar II and) Leo III. Overall the editors diagnose the whole thing as a forgery of the 'Abbasid era, but don't attribute it to the Stephen of that era.
For my part, I note that Epiphanius serves the same role for our lovable forgin' scamp Stevie as Justus and Abraham served for Jacob nuper baptizati. "Agathos Daimon" is the lucky eleventh part of the zodiac (I had to look this up; seems associated with snakes in Egypt as well, with medical undertones). "Iberia" in context means the Kartvelian part of what we call Georgia. Some modern readers might also be interested in this "new kind of state" which the Muslims brought.