Sahih Bukhari
Blood Money (Ad-Diyat)
Volume: 009 / Book Number: 083 / Hadith Number: 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)."