سَمِعْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم يَقُولُ لَهُمَا حِينَ قَرَآ كِتَابَ مُسَيْلِمَةَ مَا تَقُولاَنِ أَنْتُمَا قَالاَ نَقُولُ كَمَا قَالَ . قَالَ أَمَا وَاللَّهِ لَوْلاَ أَنَّ الرُّسُلَ لاَ تُقْتَلُ لَضَرَبْتُ أَعْنَاقَكُمَا
Muhammad Ibn Ishāq said: “Musaylimah would write to Allah’s Messenger.”
Nu’aym Ibn Mas‛ood said: I heard Allāh’s Messenger (ﷺ) say to the two emissaries of Musaylimah [the false claimant to prophethood] when he had read the letter of Musaylimah:
“What do you two say?”
They responded: “We say as Musaylimah says.”
So the Prophet Muhammad (ﷺ) said: “By Allāh, were it not for the fact that emissaries are not to be killed, I would have struck your necks.” [Reported by Abu Dāwood, no. 2761 and it is authentic.]
مَنْ قَتَلَ نَفْسًا مُعَاهَدًا لَمْ يَرَحْ رَائِحَةَ الْجَنَّةِ، وَإِنَّ رِيحَهَا يُوجَدُ مِنْ مَسِيرَةِ أَرْبَعِينَ عَامًا
Abdullāh Ibn ‛Amr narrated that Allah’s Messenger (ﷺ) said: “Whoever kills a person who is granted the agreement of protection by the Muslims shall not smell the fragrance of Paradise though its fragrance can be smelled at a distance of forty years journey.” [Reported by Bukhāree, no 6914]
The scholars of Islām have stated that it is utterly forbidden to target, harm or kill diplomats, ambassadors, emissaries and the foreign delegations of the non-Muslims and foreigners who enter the Muslim lands. It matters not how severe their enmity is towards the Muslims, since what enmity and opposition to Islam was there greater than that of Musaylimah the liar who claimed prophethood for himself whilst the Prophet Muhammad (ﷺ) was alive. This same Musaylimah who later raised an army to fight the Companions of the Prophet. And when one considers the boldness of the two emissaries that came to the Prophet of Islam, both of whom without hesitation affirmed the false claim of Musaylimah, the Prophet was clearly displeased by this great falsehood perpetrated by their leader, yet he nevertheless affirmed the principle that emissaries are not to be killed.
Shaikh Abdul-Azeez Ibn Bāz, the former Mufti of Saudi Arabia (may Allah’s mercy be upon him) was informed that there are some misguided youth who think that it is allowed to kill those non-Muslims who settle in Muslim lands as well as visitors and delegations. So he responded with a robust answer informing them that these murderous thoughts and acts are contrary to Islam, and are forbidden. He further stated that if one sees some opposition to Islam being perpetrated by the visitors or settlers, then one should inform the Muslim authorities and Muslim courts. And if there is no Islamic court, then one merely limits himself to sincerely advising the rulers, and directing them to do good, and to cooperate with them until the Islamic law is judged by. As for taking the law into one’s own hands in enjoining and forbidding people by the use of force and killing, then that is not permitted. So one is to merely cooperate with the rulers and those in authority in the land in the best possible way until they judge by the law of Allah between the people in the Muslim lands. Other than that, there is nothing more to be done than sincere advice, and directing towards good deeds. So it obligatory upon him to forbid the evil in the best manner, that is what is obligatory. Allah, the Most High, said: “Show piety and be dutiful as much as you are able.” That is because forbidding an evil by physical force in these situations by killing and striking only leads to greater evil and more corruption – and in that there is no doubt in the mind of anyone who examines these matters and knows them well.
[Abridged, see Majmoo’ Fatāwa ash-Shaikh Ibn Bāz 8/207]