http://en.wikipedia.org/wiki/Achtiname_of_Muhammad
"This is a letter which was issued by Mohammed, Ibn Abdullah, the Messenger, the Prophet, the Faithful, who is sent to all the people as a trust on the part of God to all His creatures, that they may have no plea against God hereafter. Verily God is the Mighty, the Wise. This letter is directed to the embracers of Islam, as a covenant given to the followers of Nazarene in the East and West, the far and near, the Arabs and foreigners, the known and the unknown.
This letter contains the oath given unto them, and he who disobeys that which is therein will be considered a disobeyer and a transgressor to that whereunto he is commanded. He will be regarded as one who has corrupted the oath of God, disbelieved His Testament, rejected His Authority, despised His Religion, and made himself deserving of His Curse, whether he is a Sultan or any other believer of Islam. Whenever monks, devotees and pilgrims gather together, whether in a mountain or valley, or den, or frequented place, or plain, or church, or in houses of worship, verily we are [at the] back of them and shall protect them, and their properties and their morals, by Myself, by My Friends and by My Assistants, for they are of My Subjects and under My Protection.
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They must not give anything of their income but that which pleases them—they must not be offended, or disturbed, or coerced or compelled.
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They shall not be imposed upon by anyone to undertake a journey, or to be forced to go to wars or to carry arms; for the Islams have to fight for them. Do no dispute or argue with them, but deal according to the verse recorded in the Koran, to wit: ‘Do not dispute or argue with the People of the Book but in that which is best’ [29:46]. Thus they will live favored and protected from everything which may offend them by the Callers to religion (Islam), wherever they may be and in any place they may dwell.
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...the Islams must protect them and defend them against others. It is positively incumbent upon every one of the Islam nation not to contradict or disobey this oath until the Day of Resurrection and the end of the world."