Sunan an-Nasa'i, Hadith 4748 ⓘ
It was narrated that Abu Bakrah said: The Messenger of Allah said: "Whoever kills a Mu'ahad with no justification, Allah will forbid Paradise to him and he will not even smell its fragrance."
أَخْبَرَنَا الْحُسَيْنُ بْنُ حُرَيْثٍ، قَالَ حَدَّثَنَا إِسْمَاعِيلُ، عَنْ يُونُسَ، عَنِ الْحَكَمِ بْنِ الأَعْرَجِ، عَنِ الأَشْعَثِ بْنِ ثُرْمُلَةَ، عَنْ أَبِي بَكْرَةَ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " مَنْ قَتَلَ نَفْسًا مُعَاهِدَةً بِغَيْرِ حِلِّهَا حَرَّمَ اللَّهُ عَلَيْهِ الْجَنَّةَ أَنْ يَشُمَّ رِيحَهَا " .
also referenced under: Book 45, Hadith 43 (In-Book) & Volume 5, Book 45, Hadith 4752 (DarusSalam)