I should be able to comment tonight. The troublesome creatures, my doctors, (persona non grata from now on), are here again, for nothing :-)
Having extensively visited the St. Catherine's Monastery and examined plenty of documents there for days in 1974, I never saw or heard about the exalted Prophet's reported letter there. And the staff including the deacons were very cooperative.
I suspect the authenticity of the document unless a scholar of Professor M.Rafi's caliber can come up with reliable proof - Prof Rafi Saheb especially since he posted "The Nabi's letter" for the first time on the Forum on 24 Nov 2011. See in my next post.
But then, looking closely, some facets of the proclamation made in the reported letter of the exalted Prophet contradict the Qur'an.
Contd in the next post.