Sahih al-Bukhari 3166
صحيح البخاري#3166SahihNarrated `Abdullah bin `Amr:The Prophet (ﷺ) said, "Whoever killed a person having a treaty with the Muslims, shall not smell the smell of Paradise though its smell is perceived from a distance of forty years
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Every narration in Sahih al-Bukhari is accepted as Sahih (authentic) by the established status of the book.
In-book reference: 58:8