Sahih al-Bukhari, Book 58, Hadith 8 (In-Book) ⓘ
Narrated `Abdullah bin `Amr: The Prophet 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."
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 " .
also referenced under: Hadith 3166 (DarusSalam) & Volume 4, Book 53, Hadith 391 (USC-MSA)