I saw Jabir bin ʿAbdullah swearing by Allah that Ibn Sayyad was the Dajjal. I said to Jabir, "How can you swear by Allah?" Jabir said, "I have heard ʿUmar swearing by Allah regarding this matter in the presence of the Prophet ﷺ and the Prophet ﷺ did not disapprove of it."
سَمِعْتُ عُمَرَ يَحْلِفُ عَلَى ذَلِكَ عِنْدَ النَّبِيِّ ﷺ فَلَمْ يُنْكِرْهُ النَّبِيُّ ﷺ