Sahih Bukhari
Holding Fast to the Quran and Sunnah
Volume: 009 / Book Number: 092 / Hadith Number: 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."