Narrated by Ibn Umar (Radhiallaho anho):
I heard 'Umar saying, "Allah's Messenger (sallallaahu 'alaihi wasallam) said to me,

"Allah forbids you to swear by your fathers."

Umar said, "By Allah! Since I heard that from the Prophet, I have not taken such an oath, neither intentionally, nor by reporting the oath of someone else."

Sahih Al-Bukhari Vol. 8 : No. 642