Narrated Nuaym ibn Masud: I heard the Messenger of Allah ﷺ say when he read the letter of Musaylimah: What do you believe yourselves? They said: We believe as he believes. He said: I swear by Allah that were it not that messengers are not killed, I would cut off your heads.
Explanation & Benefits
Shaykh Umar Farooq Saeedi
Benefits and Issues:
If an ambassador or envoy openly expresses disbelief (kufr) in front of the leader of the Muslims (Imam al-Muslimin), he will not be killed.
Source: Sunan Abu Dawood – Commentary by Shaykh Umar Farooq Saeedi, Page: 2761