Nafi' told that Ibn Umar used to say: I swear by Allah that I do not doubt that Antichrist is Ibn Sayyad.
Sunan Abi Dawud Book 39, Hadith 40
← Previous Hadith The prophet (ﷺ) passed by Ibn Sa’Id along with some of his companions. ‘Umar b. al-Kattab was among them. He was playing with boys near the fortress of Banu Maghalah. He was near the age of puberty (i.e. a boy). Before he was aware, the Messenger of Allah (ﷺ) gave him a pat on the back and said : Do you testify that you are the Messenger of Allah Ibn Sayyad then looked at him and said: I testify that you are the Apostle of Gentiles. Ibn Sayyad then said the prophet (ﷺ) then asked him : What comes to you ? He replied: One who speaks the truth and one who lies come to me. The prophet (may peace upon him) said: You are confused. The Messenger of Allah (may peace upon him) said to him: I have concealed something (in my hand) and he concealed the verse “the day when the sky will bring forth smoke (dukhan) clearly visible Ibn Sayyad said: It is smoke (dukhan) .The Messenger of Allah (ﷺ) said: Away with you, You cannot get farther than your rank. ‘Umar said: “Messenger of Allah, permit me to cut off his head. The Messenger of Allah (ﷺ) said: If he is the one (the Dajjal), you will not be given power over him, and if he is not, you will not do well in killing him.

Sunan Abi Dawud Book 39, Hadith 39 Next Hadith → You swear by Allah! He said: I heard Umar swearing to that in the presence of the Messenger of Allah (ﷺ), but the Messenger of Allah (ﷺ) did not make any objection to it.

Sunan Abi Dawud Book 39, Hadith 41