Sunan an-Nasa'i, Hadith 4012 ⓘ
It was narrated from 'Ubaid bin 'Umair that : His father - who was one of the Companions of the Prophet [SAW] - told him: "A man said: 'O Messenger of Allah, what are the major sins?' He said: 'They are seven; the most grievous of which are associating others with Allah, killing a soul unlawfully and fleeing (from the battlefield) on the day of the march.'" It is abridged.
أَخْبَرَنَا الْعَبَّاسُ بْنُ عَبْدِ الْعَظِيمِ، قَالَ حَدَّثَنَا مُعَاذُ بْنُ هَانِئٍ، قَالَ حَدَّثَنَا حَرْبُ بْنُ شَدَّادٍ، قَالَ حَدَّثَنَا يَحْيَى بْنُ أَبِي كَثِيرٍ، عَنْ عَبْدِ الْحَمِيدِ بْنِ سِنَانٍ، عَنْ حَدِيثِ، عُبَيْدِ بْنِ عُمَيْرٍ أَنَّهُ حَدَّثَهُ أَبُوهُ، وَكَانَ، مِنْ أَصْحَابِ النَّبِيِّ صلى الله عليه وسلم - أَنَّ رَجُلاً قَالَ يَا رَسُولَ اللَّهِ مَا الْكَبَائِرُ قَالَ " هُنَّ سَبْعٌ أَعْظَمُهُنَّ إِشْرَاكٌ بِاللَّهِ وَقَتْلُ النَّفْسِ بِغَيْرِ حَقٍّ وَفِرَارٌ يَوْمَ الزَّحْفِ " . مُخْتَصَرٌ .
also referenced under: Book 37, Hadith 47 (In-Book) & Volume 5, Book 37, Hadith 4017 (DarusSalam)