Muhammad b. Munkadir reported:As I saw Jabir b. 'Abdullah taking an oath in the name of Allah that it was Ibn Sa'id who was the Dajjal I said: Do you take an oath in the name of Allah? Thereupon he said: I heard 'Umar taking an oath in the presence of Allah's Apostle (ﷺ) to this effect but Allah's Apostle (ﷺ) did not disapprove of it

English translation · Sahih Muslim