Musannaf Ibn Abi Shayba 7:131

Abu Bakr narrated to us, he said: Sufyan ibn 'Uyaynah narrated to us, from al-Zuhri, from Salim, from his father, who said: The Prophet, peace and blessings of Allah be upon him, heard Umar saying, "And my father." The Messenger of Allah, peace and blessings of Allah be upon him, said: "Indeed, Allah forbids you from swearing by your fathers." Umar said: "By Allah, I have not sworn by them since, neither as one mentioning it nor as one reporting it."