Holding Fast to the Qur'an and Sunnah

Bukhari :: Book 9 :: Volume 92 :: Hadith 453

Narrated Muhammad bin Al-Munkadir:

I saw Jabir bin 'Abdullah swearing by Allah that Ibn Sayyad was the Dajjal. I said to Jabir, "How can you swear by Allah?" Jabir said, "I have heard 'Umar swearing by Allah regarding this matter in the presence of the Prophet and the Prophet did not disapprove of it."