'Abdur Rahman bin Al-Bailamani narrated that The Messenger of Allah (ﷺ) killed a Muslim who killed a Mu'ahid who had made a covenant with the Muslims, and said, "I am closest to the ones who keep their covenants of protection." Related by 'Abdur Razzaq. (DE)
English reference (DE): Book 9, Hadith 1214 (DE)
Arabic reference (DE): Book 9, Hadith 1184 (DE)