Sunan an-Nasa'i 4000
سنن النسائي#4000SahihIt was narrated that Sa'eed bin Jubair said:"The people of Al-Kufah differed concerning this Verse: "And whoever kills a believer intentionally." So I went to Ibn 'Abbas and asked him, and he said: 'It was revealed among the last of what was revealed, and nothing of it was abrogated after that
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 ZaiSahih - Agreed Upon
In-book reference: 37:35