Sunan an-Nasa'i 4006
سنن النسائي#4006SahihIt was narrated that Zaid bin Thabit said:"This Verse - 'And whoever kills a believer intentionally, his recompense is Hell' - was revealed six months after the Verse which was revealed in Surat Al-Furqan
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Abu GhuddahHasan Sahih
Al-AlbaniHasan Sahih
Zubair Ali ZaiHasan
In-book reference: 37:41