The sin of one who kills an innocent person having a treaty with the Muslims

Sahih al-Bukhari · Book 58 · Hadith 3166

حَدَّثَنَا قَيْسُ بْنُ حَفْصٍ، حَدَّثَنَا عَبْدُ الْوَاحِدِ، حَدَّثَنَا الْحَسَنُ بْنُ عَمْرٍو، حَدَّثَنَا مُجَاهِدٌ، عَنْ عَبْدِ اللَّهِ بْنِ عَمْرٍو ـ رضى الله عنهما ـ عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ ‏"‏ مَنْ قَتَلَ مُعَاهَدًا لَمْ يَرَحْ رَائِحَةَ الْجَنَّةِ، وَإِنَّ رِيحَهَا تُوجَدُ مِنْ مَسِيرَةِ أَرْبَعِينَ عَامًا ‏"‏‏.‏

Narrated `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."