Sunan an-Nasa'i 3768
سنن النسائي#3768SahihIt was narrated from Salim, from his father, that he told him from 'Umar:"The Messenger of Allah said: 'Allah forbids you to swear by your forefathers.'" 'Umar said: "By Allah, I never swore by them again, whether saying it for myself or reporting it of others
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: 35:8