The Prophet ﷺ said, "Whoever killed a Mu'ahid (a person who is granted the pledge of protection by the Muslims) shall not smell the fragrance of Paradise though its fragrance can be smelt at a distance of forty years (of traveling).  

عَنِ النَّبِيِّ ﷺ قَالَ مَنْ قَتَلَ نَفْسًا مُعَاهَدًا لَمْ يَرَحْ رَائِحَةَ الْجَنَّةِ وَإِنَّ رِيحَهَا يُوجَدُ مِنْ مَسِيرَةِ أَرْبَعِينَ عَامًا