The Prophet (peace and blessings be upon him) said:
"Listen! By Allah, were it not the rule that envoys (ambassadors) are not killed, I would have struck off both your necks."
Hadith Referenceصحیح الجامع الصغیر / حرف الألف / 1339
Hadith Gradingالألبانی:حسن
Hadith Takhrij[د ك] عن نعيم بن مسعود. المشكاة ٣٩٨٢.