"[F]or Almighty God, Who desires that all men shall be saved and that none shall perish, approves nothing more highly in us than this: that a man love his fellow man next to his God and do nothing to him which he would not that others should do to himself.
This affection we and you owe to each other in a more peculiar way than to people of other races because we worship and confess the same God though in diverse forms and daily praise and adore Him as the creator and ruler of this world. For, in the words of the Apostle, 'He is our peace who hath made both one.'
This grace granted to you by God is admired and praised by many of the Roman nobility who have learned from us of your benevolence and high qualities.[. . .]
For God knows our true regard for you to his glory and how truly we desire your prosperity and honor, both in this life and in the life to come, and how earnestly we pray both with our lips and with our heart that God Himself, after the long journey of this life, may lead you into the bosom of the most holy patriarch Abraham."
-- From Letter XXI of Pope St. Gregory VII (†1085) to the (Muslim) King of Mauritania: