Sahih Bukhari Volume 8, Book 78, Hadith Number 642.

Narated By Ibn ‘Umar : I heard ‘Umar saying, “Allah’s Apostle 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.”