Sunan Ibn Majah
Sunan Ibn Majah 176
حَدَّثَنَا سَهْلُ بْنُ أَبِي سَهْلٍ، حَدَّثَنَا سُفْيَانُ بْنُ عُيَيْنَةَ، عَنْ أَبِي غَالِبٍ، عَنْ أَبِي أُمَامَةَ، يَقُولُ شَرُّ قَتْلَى قُتِلُوا تَحْتَ أَدِيمِ السَّمَاءِ وَخَيْرُ قَتْلَى مَنْ قَتَلُوا كِلاَبُ أَهْلِ النَّارِ قَدْ كَانَ هَؤُلاَءِ مُسْلِمِينَ فَصَارُوا كُفَّارًا . قُلْتُ يَا أَبَا أُمَامَةَ هَذَا شَىْءٌ تَقُولُهُ قَالَ بَلْ سَمِعْتُهُ مِنْ رَسُولِ اللَّهِ ـ صلى الله عليه وسلم ـ .
Unreviewed translation. All hadiths in this collection are available in five languages. Titles and introductions may remain in Arabic.
Sahl ibn Abi Sahl reported to us: Sufyan ibn Uyaynah reported to us, from Abu Ghalib, from Abu Umamah, who said: ‘The worst of those slain under the sky are those killed by them, and the best of those slain are those killed by them. They are the dogs of the people of Hell. These people were Muslims, then became unbelievers.’ I asked, ‘Abu Umamah, is this your own statement?’ He said, ‘Rather, I heard it from the Messenger of Allah (Allah bless him and grant him peace).’
Notes and open questions — unreviewed
The Arabic says the best of those slain are those who were killed by them, and then states that they were Muslims who became unbelievers.