Hadith: Whoever kills a Mu‘āhad (a non-Muslim who is granted the pledge of protection by the Muslims) shall not smell the fragrance of Paradise, though its fragrance can be smelt at a distance of forty years (of traveling)
عن عبد الله بن عمرو رضي الله عنهما عن النبي صلى الله عليه وسلم قال: «من قَتَلَ مُعَاهَدًا لم يَرَحْ رَائحَةَ الجنة، وإن رِيْحَهَا تُوجَدُ من مَسِيرَة أربعين عامًا». [صحيح] - [رواه البخاري] المزيــد ...
‘Abdullāh ibn ‘Amr (may Allah be pleased with him) reported that the Prophet (may Allah's peace and blessings be upon him) said: "Whoever kills a Mu‘āhad shall not smell the fragrance of Paradise, though its fragrance can be smelt at a distance of forty years (of traveling).'' Sahih/Authentic. - [Al-Bukhari]
This Hadīth indicates that anyone who kills a Mu‘āhad will not be admitted to Paradise or even smell its fragrance, although its fragrance can be smelt at a distance of forty years of traveling. A Mu‘āhad is a non-Muslim who enters the lands of Muslims with a pact of security and protection, or a Dhimmi. The warning in the Hadīth proves that Islam is keen on preserving the lives of those who are given protection by Muslims, and that killing them is a major sin.
It is prohibited to kill a Mu‘āhad (a person granted the pledge of protection by Muslims). This is a major sin, for it entails the deprivation of its perpetrator from entering Paradise, as apparently indicated by the Hadīth.
Some versions of this Hadīth refer to killing 'unjustly' and 'illegally', which is a well-known restriction among the Shar‘i rules.