The hadiths in question are:

Abu Sa’id reported: I accompanied Ibn Sayyad to Mecca and he said to me: What I have gathered from people is that they think that I am Dajjal. Have you not heard Allah’s Messenger (may peace upon him) as saying: He will have no children, I said: Yes, of course. Thereupon he said: But I have children. Have you not heard Allah’s Messenger (ﷺ) as saying: He would not enter Mecca and Medina? I said: Yes, of course. Thereupon he said I have been once in Medina and now I intend to go to Mecca. And he said to me at the end of his talk: By Allah, I know his place of birth his abode where he is just now. He (Abu Sa’id) said: This caused confusion in my mind (in regard to his identity). (Sahih Muslim 2927a)

I am going to tell you about myself and I am Dajjal and would be soon permitted to get out and so I shall get out and travel in the land, and will not spare any town where I would not stay for forty nights except Mecca and Medina as these two (places) are prohibited (areas) for me and I would not make an attempt to enter any one of these two. (Sahih Muslim 2942a)

Anas bin Malik (May Allah be pleased with him) said: The Messenger of Allah (ﷺ) said, “There will be no land which will not be trampled by Dajjal (the Antichrist) but Makkah and Al-Madinah; and there will be no passage leading to them which will not be guarded by the angels, arranged in rows. Dajjal will appear in a barren place adjacent to Al- Madinah and the city will be shaken three times. Allah will expel from it every disbeliever and hypocrite.” (Riyad As Salihin 1811)

Reconciliation

Translation: He is referred to as Ibn Sayyad and also as Ibn Sa’id, and both names appear in these hadiths. His given name was Saf. The scholars said: His story is problematic and his matter is confusing—whether he is the well-known Masih al-Dajjal or someone else. There is no doubt, however, that he was a liar from among the liars (dajjal from the dajjals, dajjal in arabic means liar/deceiver).

The scholars said: The apparent meaning of the hadiths is that the Prophet, peace be upon him, was not given revelation confirming that he was the Dajjal or that he was not the Dajjal.

Rather, the Prophet was informed of the attributes of the Dajjal, and Ibn Sayyad had some possible indications that matched those. Because of that, the Prophet did not decisively declare him to be the Dajjal, nor did he decisively deny it. That is why he said to Umar, may Allah be pleased with him: “If he is him, you will not be able to kill him.”

As for Ibn Sayyad’s argument that he is Muslim and the Dajjal is a disbeliever, and that the Dajjal does not have children whereas he did, and that the Dajjal will not enter Makkah and Madinah but he did—none of this proves anything. That is because the Prophet, peace be upon him, only described those traits as true during the Dajjal’s tribulation and emergence, and the ambiguity of his story and the fact that he was one of the lying dajjals remains.

His statement to the Prophet: “Do you bear witness that I am the Messenger of Allah?”—and his claim that a spirit comes to him, sometimes truthful and sometimes lying, and that he sees a throne above water, and that he does not dislike the idea that he might be the Dajjal, and that he knows where he is now and his birthplace—and that he once became so swollen that he filled the street—all of that is part of the suspicious signs.

As for his later display of Islam, going to Hajj, participating in battle, and apparently repenting from his earlier claims—this does not decisively prove that he is not the Dajjal.

Al-Khattabi said: the early Muslims differed about him after he reached adulthood. Some narrations report that he repented from his claims and died in Madinah, and that when they wanted to pray over him, they uncovered his face so the people could see him, and they were told to testify (that he died a Muslim). It is also reported that Ibn Umar and Jabir would swear that he was the Dajjal and had no doubt about it. Jabir was told: “He embraced Islam.” He replied: “Even if he did.” They said: “He entered Makkah and was in Madinah.” He said: “Even if he did.”

Abu Dawud narrated in his Sunan with a sound chain that Jabir said: “We lost Ibn Sayyad on the day of Harrah.” This weakens the narration claiming he died in Madinah and that a prayer was held for him.

Muslim also narrated in these hadiths that Jabir ibn Abd Allah swore by Allah that Ibn Sayyad was the Dajjal, and that he heard Umar swear the same in front of the Prophet, and the Prophet did not object. Abu Dawud also narrated with a sound chain from Ibn Umar that he said: “By Allah, I do not doubt that Ibn Sayyad is the Dajjal.”

Al-Bayhaqi said in his book al-Baʿth wa al-Nushur: The people differed greatly about Ibn Sayyad—whether he was the Dajjal.

He said: Those who held that he was not the Dajjal relied on the hadith of Tamim al-Dari in the story of the Beast (Jassasah), which Muslim mentioned after this. He said: It is possible that Ibn Sayyad shared many traits with the Dajjal, just as it is authentically reported that the one who resembles the Dajjal most is ʿAbd al-ʿUzza ibn Qatan. That does not mean he is the Dajjal.

He said: The affair of Ibn Sayyad was a trial that Allah tested His servants with, and He protected the believers from it and saved them from its evil.

He said: There is nothing in the hadith of Jabir more than the Prophet remaining silent in response to Umar’s claim, so it is possible that the Prophet was still unsure about him, and then was later informed that he was not the Dajjal, as is clearly stated in the hadith of Tamim. That is the statement of al-Bayhaqi, and he inclined toward the view that Ibn Sayyad was not the Dajjal.

We have already mentioned that it is authentically narrated from Umar, Ibn Umar, and Jabir, may Allah be pleased with them, that they believed he was the Dajjal. And Allah knows best.

If it is said: Why did the Prophet not kill him, even though he claimed prophethood in his presence?—The answer has two points, as mentioned by al-Bayhaqi and others.

First, that Ibn Sayyad was not yet an adult. Qadi ʿIyad preferred this view.

Second, that this happened during the time of the truce with the Jews and their covenants. Al-Khattabi affirmed this in Maʿālim al-Sunan. He said: after the Prophet arrived in Madinah, he wrote an agreement with the Jews that they would not be harmed and would be left alone. Ibn Sayyad was one of them, or at least affiliated with them.

Sharh Sahih Muslim By An Nawawi (18/46-48)