Sunan Abi Dawud, Hadith 5228 ⓘ
Narrated AbuHurayrah: The Prophet said: We have not made peace with them since we fought with them, so he who leaves any of them alone through fear does not belong to us.
حَدَّثَنَا إِسْحَاقُ بْنُ إِسْمَاعِيلَ، حَدَّثَنَا سُفْيَانُ، عَنِ ابْنِ عَجْلاَنَ، عَنْ أَبِيهِ، عَنْ أَبِي هُرَيْرَةَ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " مَا سَالَمْنَاهُنَّ مُنْذُ حَارَبْنَاهُنَّ وَمَنْ تَرَكَ شَيْئًا مِنْهُنَّ خِيفَةً فَلَيْسَ مِنَّا " .
also referenced under: Hadith 5248 (DarusSalam) & Book 41, Hadith 5228 (USC-MSA)