Jami` at-Tirmidhi 1534
جامع الترمذي#1534SahihNarrated Ibn 'Umar:That the Messenger of Allah (ﷺ) came across 'Umar while he was on his mount, and he was swearing by his father. So the Messenger of Allah (ﷺ) said: "Verily Allah prohibits you from swearing by your fathers. So let the one who swears, swear by Allah, or be silent
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Ahmad Muhammad ShakirSahih
Al-AlbaniSahih
Bashar Awad MaaroufHasan Sahih
Zubair Ali ZaiSahih - Agreed Upon
In-book reference: 20:12