Tamim al-Dari

Tamīm al-Dārī was a Christian from one of the Christian tribes of the north who came to Madinah among the delegations of the ninth year and embraced Islam. He is remembered above all for the account the Prophet ﷺ gathered the people in the masjid to hear from him: that he and thirty men of Lakhm and Judhām had been driven off course at sea for a month, landed on an island, met a hairy beast that called itself al-Jassāsah, and were led by it to a giant bound in iron who questioned them about the date palms of Baysān, the lake of Ṭabariyyah and the spring of Zughar, and about the unlettered Prophet, and then declared himself to be the Dajjāl.

The Prophet ﷺ called the people to the masjid with al-ṣalātu jāmiʿah, said plainly that this was no sermon or lesson but the story of a Christian who had become Muslim, and used it to confirm what he had already taught them: that the Dajjāl will not enter Makkah or Ṭaybah. The report is narrated in Ṣaḥīḥ Muslim on the authority of Fāṭimah bint Qays, and a minority of scholars have questioned it, see the story for the shaykh's discussion.