Imam At-Tirmidhi reports via Abu Hurayrah the following hadith:
Rasulullah (saaws) said, “The night and the day shall not cease until a man amongst the Mawaali named Jahjaah will reign.”
This hadith is also reported by Imam Muslim in his Sahih. Imam An-Nawawi also states in his commentary that in some manuscripts of Sahih Muslim the name is actually spelled: الْجَهْجَهَا Al-Jahjahaa, which adds the “haa”.
The word Mawaali is the plural form of the word mawlaa الْمَوْلَى, and according to the commentary Tuhfat Al-Ahwadhi it means slaves (mamaaleek / الْمَمَالِيكُ ).
This is certainly a prophesy from the Prophet Muhammad (‘alayhis salam). I have not found, however, a prominent leader in history from the mawaali named jahjaah.