Sunan an-Nasa'i 3986
سنن النسائي#3986SahihIt was narrated that 'Abdullah bin 'Amr bin Al-'As said:"The Messenger of Allah [SAW] said: 'By the One in Whose Hand is my soul, killing a believer is more grievous before Allah than the extinction of the whole world
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Abu GhuddahSahih
Al-AlbaniSahih
Zubair Ali ZaiHasan
In-book reference: 37:21