“do you know about the visit of Muhammad to the abbey?”
I have no reason to believe any such visit took place since there were no “abbeys” in Arabia to speak of. There is no credible evidence at all that Muhammad ever left Arabia.
What you are thinking of - I bet - is this: http://en.wikipedia.org/wiki/Ashtiname_of_Muhammad
It’s a forgery.
1) Muhammad never went to Egypt.
2) After the Hegira, Muhammad was constantly at war. Going on a trip to Egypt was unlikely as all get out.
3) There is no reason to believe Christian monks in a country not yet conquered by Muslims would feel the need to get a promise of protection from someone who was not even in their country and who they had probably never even heard of at that time.
4) Such forged charters granting protection to monasteries were not uncommon in the Middle Ages.
As Robert Spencer wrote:
The document to which Considine is referring, the Achtiname, is of even more doubtful authenticity than everything else about Muhammads life. Muhammad is supposed to have died in 632; the Muslims conquered Egypt between 639 and 641. The document says of the Christians, No one shall bear arms against them. So were the conquerors transgressing against Muhammads command for, as Considine puts it, no Muslim to fight against his Christian brother or sister? Did Muhammad draw up this document because he foresaw the Muslim invasion of Egypt? There is no mention of this document in any remotely contemporary Islamic sources; among other anomalies, it bears a drawing of a mosque with a minaret, although minarets werent put on mosques until long after the time Muhammad is supposed to have lived, which is why Muslim hardliners consider them unacceptable innovation (bida).
The document exempts the monks of St. Catherines monastery from paying the jizya. While it is conceivable that Muhammad, believing he bore the authority of Allah, would exempt them from an obligation specified by Allah himself in the Quran (9:29), the Achtiname specifies that Christians of Egypt are to pay a jizya only of twelve drachmas.
Yet according to the seventh-century Coptic bishop John of Nikiou, Christians in Egypt came to the point of offering their children in exchange for the enormous sums that they had to pay each month.
The Achtiname, in short, bears all the earmarks of being an early medieval Christian forgery, perhaps developed by the monks themselves in order to protect the monastery and Egyptian Christians from the depredations of zealous Muslims.
No, this is definitely not what I read, nothing even remotely close.