Letters of the Prophet (PBUH)

In the six year A.H., the Prophet (s.a.a.w.) decided to send messages to the kings beyond Arabia calling them to Islam. The Prophet attached great importance to this initiative. These messengers were going to distant lands with whom there was no agreement or treaty. They did not know the languages of these lands nor anything about the ways and disposition of their rulers. They were to invite these rulers to give up their religion and forsake their power and glory and enter the religion of a people who shortly before were almost their subjects. The mission was undoubtedly hazardous.
To make known his plan, the Prophet (s.a.a.w.) called his companions together and addressed them. He started by praising God and thanking Him. He then recited the Shahadah and went on:
"I want to send some of you to the rulers of foreign lands but don't dispute with me as the Israelites disputed with Jesus, the son of Mary.
"O Prophet of God, we shall carry out whatever you wish," they responded. "Send us wherever you desire."
The Prophet commissioned six of his Sahabah to carry his letters to Arab and foreign rulers. In order to authenticate the credentials of his envoys, a silver seal was made in which were graven the words: “ Muhammad the Messenger of Allâh.” Prophet Muhammad (s.a.a.w.) himself was unlettered, so the writings of his messages were done by Sahabah. Envoys were chosen on the basis of their experience and knowledge, and sent on their errands in Muharram in the year 7 A.H., a few days before heading for Khaibar.