The Messenger of Allah ﷺ said, "Whoever kills a person under a covenant of protection without just cause, Allah will forbid him from even smelling the fragrance of Paradise."
قال رسول الله ﷺ: من قتل نفسا معاهدة بغير حلها حرم الله عليه الجنة أن يجد ريحها.
Ahmad (20383) narrated it from Waki, who said, Sufyan told us, from Yunus bin Ubayd, from Hakam bin Aaraj, from Ashath bin Tharmala, from Abu Bakra, who said, then he mentioned it.Its chain is hasan because of Ashath bin Tharmala, and the discussion of him is set out at length in the Book of the People of the Covenant (Ahl al-Dhimma).Abdul-Razzaq (10/102) also narrated it from Sufyan Thawri with the same chain, adding, "and its smell can be detected from a distance of one hundred years' journey."There are other hadiths on this subject mentioned in the Book of Retaliation and the Book of the Rulings Concerning the People of the Covenant.