Musnad Ahmad 27:146

Sufyan narrated to us, from Isma'il ibn Umayyah, from Nafi', from Ibn 'Umar: The Messenger of Allah (ﷺ) caught up with 'Umar while he was on one of his journeys, and he was saying, "And my father, and my father." He said: "Indeed, Allah forbids you from swearing by your fathers. So whoever is to take an oath, let him swear by Allah, or else let him remain silent."