Sayyiduna Alya' al-Sulami (may Allah be pleased with him) said: I heard the Messenger of Allah (peace and blessings be upon him) say: "The Hour will not be established until a man from among the freed slaves becomes ruler over the people; he will be called 'Jahjah'."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 15248