بسم الله الرحمن الرحيم
The great Shia scholar in the field of hadith; Muhaddith al-Nūrī at-Ṭabarsī has mentioned in his book; ''Nafas al-Raḥmān fī faḍāʼil Salmān'', after researching about Dajjal, Khorasani and Yamani in Shia hadith, he has said the following about al-Yamani:
واليماني من اليمن
and [the emergence of] al-Yamani from Yemen.
Source: Nafas al-Raḥmān by Muhaddith al-Nūrī at-Ṭabarsī, page 289,
 I say: May Allah bless at-Ṭabarsī (ra), for he has said the truth about al-Yamani, and al-Sadiq (as) has said in a Ṣaḥīḥ [authentic] hadith, that al-Yamani will emerge from Yemen with the white flags. - [Read Here].
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