
Muhmmad is Considered as the Founder of Islam and The Final Prophet of God(According to Islam ).One of The Key Factor of Islam compared to Any other Religion that rose in Antiquity is that it rose in ”The Light of History ” , That is to say to Compared to any other religion that rose before islam have no Contemperory Witnesses and Confession.for example if we take the example of Christianity for Jesus as Historical Person- we have no first century A.D Witness in material as well as Quotation though rare readable mention from Tacitus (Roman Historian) and Josephus (Jewish traitor ) are often quoted, they all come from 2nd Century A.D with no material documents from the same period.
Incase of Muhammad and islam-We have Library of Sources from variety of language stretches from Syriac,Latin,Persian,Armenian,Coptic,Greek…etc
Out of Which Early Christian Witness mount to Large corpus of Description and Mentions,
Below is one among Most Important Witnesses from the Period 1st Century A.H- i,e. 7th Century A.D. on the rise of Islam and Arab’s Liberation of Jerusalem from Romans(Byzantine)
Point to note – the Witness writes in christian point of view – that is to say how Christians saw invaders and their origin
Sophronius, Patriarch of Jerusalem (d. ca. 639)
Intro :Sophronius (c. 560 – March 11, 638; Greek: Σωφρόνιος) was the Patriarch of Jerusalem from 634 until his death, and is venerated as a saint in the Eastern Orthodox and Catholic Churches. Before rising to the primacy of the see of Jerusalem, he was a monk andtheologian who was the chief protagonist for Orthodox teaching in the doctrinal controversy on the essential nature of Jesus and his volitional acts.(Wikipedia)

In a synodical letter without date, Sophronius gives an extensive list of heretics and asks, in the valedictions, that the following may be granted by God to “our Christ-loving and most gentle emperors”:]
a strong and vigorous sceptre to break the pride of all the barbarians, and especially of the Saracens who, on account of our sins, have now risen up against us unexpectedly and ravage all with cruel and feral design, with impious and godless audacity. More than ever, therefore, we entreat your Holiness to make urgent petitions to Christ so that he, receiving these favourably from you, may quickly quell their mad insolence and deliver these vile creatures, as before, to be the footstool of our God-given emperors. (Ep. synodica, PG 87, 3197D-3200A [p. 69])

[The following comments are dated to December of 634.]
We, however, because of our innumerable sins and serious misdemeanours, are unable to see these things, and are prevented from entering Bethlehem by way of the road. Unwillingly, indeed, contrary to our wishes, we are required to stay at home, not bound closely by bodily bonds, but bound by fear of the Saracens. (Christmas Sermon, 506 [p. 70])
At once that of the Philistines, so now the army of the godless Saracens has captured the divine Bethlehem and bars our passage there, threatening slaughter and destruction if we leave this holy city and dare to approach our beloved and sacred Bethlehem. (Christmas Sermon, 507 [p. 70]
If we were to live as is dear and pleasing to God, we would rejoice over the fall of the Saracen enemy and observe their near ruin and witness their final demise. For their blood-loving blade will enter their hearts, their bow will be broken and their arrows will be fixed in them. (Christmas Sermon, 515 [p. 71])
[This dates to the 6th of December in 636 or 637.]
But the present circumstances are forcing me to think differently about our way of life, for why are [so many] wars being fought among us? Why do barbarian raids abound? Why are the troops of the Saracens attacking us? Why has there been so much destruction and plunder? Why are there incessant outpourings of human blood? Why are the birds of the sky devouring human bodies? Why have churches been pulled down? Why is the cross mocked? Why is Christ, who is the dispenser of all good things and the provider of this joyousness of ours, blasphemed by pagan mouths (ethnikois tois stomasi) so that he justly cries out to us: “Because of you my name is blasphemed among the pagans,” and this is the worst of all the terrible things that are happening to us. That is why the vengeful and God-hating Saracens, the abomination of desolation clearly foretold to us by the prophets, overrun the places which are not allowed to them, plunder cities, devastate fields, burn down villages, set on fire the holy churches, overturn the sacred monasteries, oppose the Byzantine armies arrayed against them, and in fighting raise up the trophies [of war] and add victory to victory. Moreover, they are raised up more and more against us and increase their blasphemy of Christ and the church, and utter wicked blasphemies against God. Those God-fighters boast of prevailing over all, assiduously and unrestrainably imitating their leader, who is the devil, and emulating his vanity because of which he has been expelled from heaven and been assigned to the gloomy shades. Yet these vile ones would not have accomplished this nor seized such a degree of power as to do and utter lawlessly all these things, unless we had first insulted the gift [of baptism] and first defiled the purification, and in this way grieved Christ, the giver of gifts, and prompted him to be angry with us, good though he is and though he takes no pleasure in evil, being the fount of kindness and not wishing to behold the ruin and destruction of men. We are ourselves, in truth, responsible for all these things and no word will be found for our defence. What word or place will be given us for our defence when we have taken all these gifts from him, befouled them and defiled everything with our vile actions? (Holy Baptism, 166-167 [pp. 72-73])
[In a work originally composed by John Moschus (d. 619), but expanded by Sophronius (d. ca. 639), actually found only in an addition of the Georgian translation, the following entry appears, concerning a construction dated by tradition at 638, i.e., soon after the capture of Jerusalem ca. 637. It appears in a portion concerning Sophronius as recounted on the authority of his contemporary, the archdeacon Theodore, and may have been written down ca. 670.]
the godless Saracens entered the holy city of Christ our Lord, Jerusalem, with the permission of God and in punishment for our negligence, which is considerable, and immediately proceeded in haste to the place which is called the Capitol. They took with them men, some by force, others by their own will, in order to clean that place and to build that cursed thing, intended for their prayer and which they call a mosque (midzgitha). (Pratum spirituale, 100-102 [p. 63])
Source ;
Seeing islam as other saw it – Robert Hoyland