Letter to All Christians from Prophet Muhammad
How should Muslims treat Christians? With violence? Anger? Hatred? The answer is none of the above.
In a time when tensions between Islam and Christianity seem to be at an all time high, we remind our Christian friends that a true Muslim cannot hurt a Christian in any way, neither by his hand, nor by his tongue.
Below is the English translation of a letter that many academics say was narrated by the Prophet Muhammad (pbuh) in the year 628. The original letter is now in the Topkapi Museum in Instanbul.
“This is a message from Muhammad ibn Abdullah, as a covenant to those who adopt Christianity, near and far, we are with them. Verily I, the servants, the helpers, and my followers defend them, because Christians are my citizens; and by Allah! I hold out against anything that displeases them.
No compulsion is to be on them. Neither are their judges to be removed from their positions nor their monks from their monasteries.
No one is to destroy a house of their religion, to damage it, or to carry anything from it to the Muslims’ houses. Should anyone take any of these, he would spoil God’s covenant and disobey His Prophet. Verily, they are my allies and have my secure charter against all that they hate.
No one is to force them to travel or to oblige them to fight. The Muslims are to fight for them. If a female Christian is married to a Muslim, it is not to take place without her approval. She is not to be prevented from visiting her church to pray.
Their churches are to be respected. They are neither to be prevented from repairing them nor the sacredness of their covenants. No one of the nation (Muslims) is to disobey the covenant till the Last Day (end of the world).” 
A lot of academic work has been done in discussing the possible authenticity of this letter. There are different sources that mention the tradition associated with it, such as the one mentioned in a well known article by Dr. Aziz Suryal Atiya (The monastery of St. Catherine and the Mount Sinai Expedition). Dr. Atiya was a professor of Medieval History at Farouk I University. A relevant excerpt is cited below:
“After the Arab conquest of Egypt in AD 640, it is said that the Prophet Muhammad granted the monks of Mount Sinai a covenant whereby their lives and property became secure under Muslim rule. The existing tradition is that the original charter was taken from the Monastery by Sultan Selim I after the Ottoman conquest of Egypt in 1517. The Sultan, however, gave the monks a copy of it and sanctioned its terms. On the other hand, it is clear from the monumental collection of ancient and modern scrolls preserved in the Monastery Library that the Covenant of the Prophet, whether authentic or forged, was in some way or other renewed” 
Whether this document was a reflection of the sentiments of much later rulers, including some later redactions, or a document contrived by the early Christians to vouchsafe their own protection under Muslim rule will always be questioned by critics. However, the fact that the monastery survives today in tact is a testimony that it had some kind of protection afforded to it throughout its existence under different Muslim rulers. It even includes a mosque from the 12th century inside its premises which speaks volumes of religious tolerance during its existence.
 English translation from ‘Muslim History: 570 - 1950 C.E.’ by Dr. A. Zahoor and Dr. Z. Haq, ZMD Corporation. P.O. Box 8231 - Gaithersburg, MD 20898-8231 - Copyright Akram Zahoor 2000. P. 167
 ATIYA A.S. The Monastery of St. Catherine and the Mount Sinai Expedition, Read April 19, 1951, included in Proceedings of the American Philosophical society Vol 96, No, 5, October 1952, page 578