Narrated It was narrated that ʼUmar رضي الله عنه said:
The Messenger of Allah (ﷺ) heard me swearing an oath by my father and said: “Allah forbids you to swear by your fathers.” ‘Umar said: By Allah, I never swore by my father after that, whether saying it myself or narrating what someone else had said.
We were with `Utbah bin Farqad and `Umar رضي الله عنه wrote to him about things he narrated from the Prophet (ﷺ). Among the things he wrote was that the Messenger of Allah (ﷺ) said: `No one wears silk in this world except one who will not wear it in the Hereafter, except this much,` and he gestured with his two fingers, the forefinger and the middle finger. Abu `Uthman said: I thought this referred to the edging of the tayalisah (a shawl-like garment) when we first saw the tayalisah.
Narrated It was narrated that Ibn ‘Abbas said; ‘Umar said:
I was walking with a group of people during a campaign I went on with the Messenger of Allah (ﷺ) and I swore an oath, saying, No, by my father. A man behind me rebuked me for that and said: “Do not swear by your fathers,” I turned around and saw that it was the Messenger of Allah (ﷺ).