What is the Hadith of Al-Jassasah, what are the meanings of its unusual words, and what are the most prominent lessons derived from it?

The Hadith of Al-Jassasah was narrated by Imam Muslim in his Sahih, on the authority of Fatimah bint Qays. In it, Tamim al-Dari, a Christian who embraced Islam, recounted to the Prophet (peace be upon him) his story with the Dajjal. Tamim, along with thirty men, boarded a ship. The waves tossed them for a month until they reached an island. There, they met a hairy beast called Al-Jassasah, which informed them that a man in the monastery was awaiting their news.

They went to the monastery and found therein the greatest human being they had ever seen in creation, and the most heavily bound. They asked him, "Who are you?" He replied, "I am the Masih (the Dajjal)." He then questioned them about the palm trees of Baysan, Lake Tiberias, and the spring of Zughar, and about the Prophet of the unlettered people and what he had done. They informed him that he had departed from Makkah and settled in Yathrib, fought the Arabs, prevailed over those near him, and they obeyed him.

Then the Dajjal said: "Indeed, I am the Masih. And it is about to be permitted for me to emerge. So, I will come out and travel through the earth, leaving no village but that I will enter it within forty nights, except Makkah and Taybah. Both are forbidden to me. Whenever I intend to enter either of them, an angel with a unsheathed sword will confront me, preventing me from entering. And indeed, over every passage leading to them, there are angels guarding them."

Then the Messenger of Allah (peace be upon him) said: "This is Taybah," meaning Madinah. He then stated that Tamim's account concurred with what he had been telling them about him, Madinah, and Makkah, and that the Dajjal is in the sea of Sham (Syria) or the sea of Yemen, or from the direction of the East.