Musannaf Ibn Abi Shaybah

Hazrat Ibn Abbas (may Allah be pleased with both of them) wrote a letter to a person from among the People of the Book, and he wrote "As-Salaam Alaik" (peace be upon you).

Hazrat Mansur (may Allah have mercy on him) says that I asked Ibrahim (may Allah have mercy on him) and Hazrat Mujahid (may Allah have mercy on him) how a letter should be written to the dhimmis. Hazrat Mujahid said: It should be written to them: "As-salamu 'ala man ittaba'a al-huda" (Peace be upon him who follows guidance), and Ibrahim said: Write "Salam 'alaik" (Peace be upon you).

Hazrat Abu Huraira (may Allah be pleased with him) narrates that the Holy Prophet (peace and blessings be upon him) wrote a letter to a person from among the People of the Book, in which he wrote: "Accept Islam, you will be safe." The Prophet (peace and blessings be upon him) had not yet finished writing the letter when a letter from that person arrived. It was read out, and it contained greetings (salaam). So the Holy Prophet (peace and blessings be upon him) also replied to the greeting at the end of his letter.

It is narrated from Hazrat Aamir (may Allah be pleased with him) that Hazrat Khalid bin Waleed (may Allah be pleased with him) wrote a letter from the place of Heerah to the Marzban of Persia as follows: In the name of Allah, the Most Gracious, the Most Merciful. From Khalid bin Waleed to the Marzban of Persia. Peace be upon him who follows guidance.