Sunan an-Nasa'i 4012
سنن النسائي#4012HasanIt 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
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Abu GhuddahHasan
Al-AlbaniHasan
Zubair Ali ZaiHasan
In-book reference: 37:47