Sunan an-Nasa'i 4747
سنن النسائي#4747Sahihأَخْبَرَنَا إِسْمَاعِيلُ بْنُ مَسْعُودٍ، قَالَ حَدَّثَنَا خَالِدٌ، عَنْ عُيَيْنَةَ، قَالَ أَخْبَرَنِي أَبِي قَالَ، قَالَ أَبُو بَكْرَةَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " مَنْ قَتَلَ مُعَاهِدًا فِي غَيْرِ كُنْهِهِ حَرَّمَ اللَّهُ عَلَيْهِ الْجَنَّةَ " .
Abu Bakrah said:"The Messenger of Allah said: 'Whoever kills a Mu'ahad with no justification, Allah will forbid Paradise to him
Scholarly Authentication
The label above is the grade most of these scholars gave — one dissenting opinion no longer speaks for all of them. If any scholar calls a narration fabricated, that verdict is shown instead, whatever the others say. Each scholar's own wording:
Abu GhuddahSahih
Al-AlbaniSahih
Zubair Ali ZaiIsnaad Sahih
In-book reference: 45:42