Blood Money (Ad-Diyat)
Bukhari :: Book 9 :: Volume 83 :: Hadith 49
Narrated 'Abdullah bin 'Amr:
The Prophet said, "Whoever killed a Mu'ahid (a person 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)."