Running through the main authority on this topic, Hoyland's
Seeing Islam as Others Saw It, and looking just at the seventh century.
Teachings of Jacob, Greek antisemitic tract representing orthodox imperial opinion, c. 634:
[The Jews] were saying that the prophet had appeared, coming with the Saracens, and that he was proclaiming the advent of the anointed one, the Christ who was to come. I, having arrived at Sykamina, stopped by a certain old man well-versed in the scriptures, and I said to him: "What can you tell me about the prophet who has appeared with the Saracens?" He replied, groaning deeply: "He is false, for the prophets do not come armed with a sword. Truly they are works of anarchy being committed today and I fear that the first Christ to come, whom the Christians worship, was the one sent by God and we instead are preparing to receive the Antichrist. Indeed, Isaiah said that the Jews would retain a perverted and hardened heart until all the earth should be devastated. But you go, master Abraham, and find out about the prophet who has appeared." So I, Abraham, inquired and heard from those who had met him that there was no truth to be found in the so-called prophet, only the shedding of men's blood. He says also that he has the keys of paradise, which is incredible.
Appendix to Roman monk John Moschus's
Pratum Spirituale, 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 midzgitha [Arabic for mosque is masjid].
Sermon of Sophronius, Patriarch of Jerusalem, c. 634:
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 Roman 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. These 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.
The general view was that the Arabs were clearly God's terrible punishment for the sins of the Romans.