The Messenger of Allah ﷺ said, "Whoever kills a man from the people under covenant of protection will not find the fragrance of Paradise, though its fragrance can be detected from a distance of seventy years' travel."
حدثنا وكيع حدثنا أبي عن منصور عن هلال بن يساف عن القاسم بن مخيمرة
قال رسول الله ﷺ من قتل رجلا من أهل الذمة لم يجد ريح الجنة وإن ريحها ليوجد من مسيرة سبعين عاما
Its isnad is sahih. Waki's father is Jarra bin Mulayh, a well-known trustworthy narrator. Mansur is Ibn Mutamir. Hilal bin Yasaf is trustworthy, as mentioned many times before, and likewise Qasim bin Mukhaymara Shami, who is among the trustworthy Successors.The hadith was narrated by Nasai, 8/25, no. 4749, in the book of Qasama, chapter on the gravity of killing a person under covenant, through the route of Shuba, from Mansur, from him, with this wording, and similarly with a close wording from Abdullah bin Amr, no. 4750. Likewise Hakim, 2/142, and Dhahabi agreed with him. The senior imams narrated it with similar wording. See Sahih Bukhari, 9/16, in the book of blood money, chapter on the sin of killing a non-Muslim under protection without cause, Sunan Abu Dawud, 3/83, no. 2760, in the book of jihad, and Ibn Majah, 2/896, no. 2686, in the book of blood money.