The one who tells it is Fâtima bint Qays (may Allah be pleased with her), one of the first women to emigrate.
She heard the call “as-salâtu jâmi'a”, prayer in congregation, and went out to the mosque.
She prayed in the women's row. When the prayer ended, the Prophet ﷺ sat on the minbar, laughing.
“Let everyone stay where he prayed.” Then: “Do you know why I gathered you?”
They said: “Allah and His Messenger know best.”
“By Allah, I did not gather you for something to hope for, nor for something to fear.”
“I gathered you because Tamîm ad-Dârî was a Christian man. He came, pledged allegiance and became Muslim.”
“And he told me something that agrees with what I used to tell you about the Masîh ad-Dajjâl.”
Who was Tamîm (may Allah be pleased with him)? The hadith gives one line: a Christian who came and became Muslim.
The biographers add that he lived in Palestine, in the land of Shâm, and traded there. The hadith does not say so.
Accounts also tell of his search: a rabbi, a priest, even a jinn. Their chains are not verified.
Tamîm told that he boarded a sea-going ship with thirty men of Lakhm and Judhâm.
The waves played with them for a month at sea.
Then they reached an island in the sea, at sunset.
They sat in the ship's small boats, and went onto the island.
A creature met them, so thick with hair that they could not tell its front from its back.
They said: “Woe to you, what are you?” It said: “I am al-Jassâsa.”
The scholars link the name to tajassus, seeking out news. The hadith itself does not explain it.
It said: “Go to this man in the monastery. He longs for your news.”
Tamîm said: when it named a man for us, we were afraid it might be a she-devil.
So they went in haste, until they entered the monastery.
One day in Medina, a crier called the people to the mosque.
The Prophet ﷺ sat on the minbar, laughing. What did he want to tell them?
Asked about the unseen, the companions answered: “Allah and His Messenger know best.”
Tonight, before you share a story about the end times, ask one question: where is it reported?