ENOfficial
Muhammad b. al-Munkadir told that he saw Jabir b. `Abdallah swearing by God that Ibn as-Sayyad was the dajjal, and when he expressed surprise that he should, swear by God, he replied that he had heard `Umar swearing to that in the Prophet's presence without the Prophet (ﷺ) making any objection to it. (Bukhari and Muslim.)
Source: sunnah.com
Other translations
Arabic
وَعَنْ مُحَمَّدِ بْنِ الْمُنْكَدِرِ قَالَ: رَأَيْتُ جَابِرَ بْنَ عَبْدِ اللَّهِ يَحْلِفُ بِاللَّهِ أَنَّ ابْنَ الصَّيَّادِ الدَّجَّالُ. قُلْتُ: تَحْلِفُ بِاللَّهِ؟ قَالَ: إِنِّي سَمِعْتُ عُمَرَ يَحْلِفُ عَلَى ذَلِكَ عِنْدَ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ فَلَمْ يُنْكِرْهُ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ. مُتَّفَقٌ عَلَيْهِ
sunnah.com