that Abu Sufyan bin Harb informed him that Hiraql had sent for him while he was with a party of the Quraish, and they were trading in Ash-Sham, so they went to him." And he mentioned the Hadith and said: "Then he called for the letter of the Messenger of Allah (ﷺ) to be read, and it said in it: 'In the Name of Allah, the Merciful, the Beneficent. From Muhammad, Allah's Slave and His Messenger, to Hiraql the leader of Rome. Peace be upon whoever follows the guidance. To proceed:"
Jami` at-Tirmidhi Book 42, Hadith 30
← Previous Hadith "Before he died, the Messenger of Allah (ﷺ) had written to Kisra, Ceasar, An-Najashi, and to every tyrant calling them to Allah. This An-Najashi is not the one that the Prophet (ﷺ) performed to the funeral Salat for."

Jami` at-Tirmidhi Book 42, Hadith 29 Next Hadith → "When the Prophet of Allah (ﷺ) wanted to write to the foreigners, it was said to him: 'The foreigners do not accept a letter unless it has a seal.' So he had a ring made." He said: "It is as if I am now looking at its whiteness in his hand."

Jami` at-Tirmidhi Book 42, Hadith 31