‘Umar b. Khattab went along with Allah’s Messenger (ﷺ) in the company of some persons to Ibn Sayyad that he found him playing with children near the battlement of Bani Maghala and Ibn Sayyad was at that time just at the threshold of adolescence and he did not perceive (the presence of Holy Prophet) until Allah’s Messenger (ﷺ) struck his back with his hands. Allah’s Messenger (ﷺ) said: Ibn Sayyad, don’t you bear witness that I am the messenger of Allah? Ibn Sayyad looked toward him and he said: I bear witness to the fact that you the messenger of the unlettered. Ibn Sayyad said to the Allah’s Messenger (ﷺ): Do you bear witness to the fact that I am the messenger of Allah? Allah’s Messenger (ﷺ) rejected this and said: I affirm my faith in Allah and in His messengers. Then Allah’s Messenger (ﷺ) said to him: What do you see? Ibn Sayyad said: It is a Dukh. Thereupon Allah’s Messenger (ﷺ) said: May you be disgraced and dishonoured, you would not not be able to go beyond your rank. ‘Umar b. Khattab said: Allah’s Messenger, permit me that I should strike his neck. Thereupon Allah’s Messenger (ﷺ) said: If he is the same (Dajjal) who would appear near the Last Hour, you would not be able to overpower him, and if he is not that there is no good for you to kill him. ‘Abdullah b. ‘Umar further narrated that after some time Allah’s Messenger (ﷺ) and Ubayy b. Ka’b went towards the palm trees where Ibn Sayyad was.
When Allah’s Messenger (ﷺ) went near the tree he hid himself behind a tree with the intention of hearing something from Ibn sayyad before Ibn Sayyad could see him, but Allah’s Messenger (ﷺ) saw him on a bed with a blanket around him from which a murmuring sound was being heard and Ibn Sayyad’s mother saw Allah’s Messenger (ﷺ) behind the trunk of the palm tree. She said to Ibn Sayyad: Saf (that being his name), here is Muhammad. Thereupon Ibn Sayyad jumped up murmuring and Allah’s Messenger (ﷺ) said: If she had left him alone he would have made things clear. Abdullah b. Umar told that Allah’s Messenger (ﷺ) stood up amongst the people and lauded Allah as He deserved, then he made a mention of the Dajjal and said: I warn you of him and there is no Prophet who has not warned his people against the Dajjal. Even Noah warned (against him) but I am going to tell you a thing which no Prophet told his people. You must know that he (the Dajjal) is one-eyed and Allah, the Exalted and Glorious, is not one-eyed. Ibn Shihab said: ‘Umar b. Thabit al-Ansari informed me that some of the Companions of Allah’s Messenger (ﷺ) informed him that the day when Allah’s Messenger (ﷺ) warned people against the Dajjal, he also said: There would be written between his two eyes (the word) Kafir (infidel) and everyone who would resent his deeds would be able to read or every Muslim would be about to read, and he also said: Bear this thing in mind that none amongst you would be able to see Allah, the Exalted and Glorious, until he dies.(Sahih Muslim, Book 41, Hadith #7000)
This narration clearly shows that the Holy Prophet Muhammad(saw) was not sure whether he was Dajjal or not. This itself shows us that Muhammad(saw) was told about Dajjal in his revelations, but the actual identity was not fully disclosed to him. If the actual identity was revealed to him, then he would have either confirmed or denied that Ibn Sayyad was that Dajjal prophesied. The Holy Prophet Muhammad(saw) was told the attributes of Dajjal and even what to read to be protected from it but not the entire reality.