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

The Prophet (may Allah's peace and blessings be upon him) demonstrates the stern warning to anyone who kills a mu‘āhad - a non-Muslim who comes from the land of disbelievers to the abode of Islam and receives the pledge of protection and security - that he will not smell the fragrance of Paradise, though its fragrance can be smelt at a distance of forty years journey.

1. It is prohibited to kill a mu‘āhad, a dhimmi, or a musta’man. This is a major sin.
2. Mu‘āhad: He is a disbeliever with whom a covenant was made while he lives in his land and does not fight the Muslims, nor do they fight him. Dhimmi: He is a non-Muslim who comes to live in the Muslim land and pays tribute. Musta’man: He is a non-Muslim who enters the land of the Muslims under a covenant and pledge of protection for a certain period of time.
3. It warns against the betrayal of covenants with non-Muslims.

صحيح البخاري منحة العلام في شرح بلوغ المرام، لعبد الله الفوزان (8/ 232). توضيح الأحكام شرح بلوغ المرام، للبسام (6/ 90). فتح ذي الجلال والإكرام بشرح بلوغ المرام، لابن عثيمين (5/ 520). سبل السلام، لمحمد الصنعاني (2/ 501).