Sunan Ibn Majah, Volume 3, Book 21, Hadith 2686 (DarusSalam) ⓘ
It was narrated from 'Abdullah bin 'Amr that the Messenger of Allah said: “Whoever kills a Mu'ahid, will not smell the fragrance of Paradise, even though its fragrance may be detected from a distance of forty years.”
حَدَّثَنَا أَبُو كُرَيْبٍ، حَدَّثَنَا أَبُو مُعَاوِيَةَ، عَنِ الْحَسَنِ بْنِ عَمْرٍو، عَنْ مُجَاهِدٍ، عَنْ عَبْدِ اللَّهِ بْنِ عَمْرٍو، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " مَنْ قَتَلَ مُعَاهِدًا لَمْ يَرَحْ رَائِحَةَ الْجَنَّةِ وَإِنَّ رِيحَهَا لَيُوجَدُ مِنْ مَسِيرَةِ أَرْبَعِينَ عَامًا " .
also referenced under: Hadith 2686 (Reference) & Book 21, Hadith 2788 (In-Book)