Imam Reza (PBUH) (8th Imam of Shia, from the descendant of Prophet Muhammad (PBUH)) has said, in the course of a Hadith, “The Imam after me is my son, Muhammad (Imam Muhammad Jawad), and after him his son Ali (Imam Ali Hadi), and after Ali his son, Hassan (Imam Hassan Askari), and after Hassan his son Hujjat Al-Qa’im (the risen reason), who is awaited during his occultation and obeyed during his manifestation. If there remain from the life of the world but a single day, Allah (God) will extend that day until he becomes manifest, and fill the world with justice in the same way that it had been filled with iniquity. But when? As for news of the hour, verily my father told me, having heard it from his father who heard it from his father who heard it from his ancestors who heard it from Imam Ali (PBUH), that it was asked of the Holy Prophet, “Oh Prophet of Allah, when will the “Qa’im” (the Risen) who is from thy family appear?” He said, “His case is unknown like the Resurrection day. He will manifest it at its proper time. It is significant in the heavens and the earth. It cometh not to you save unawares”
(Holy Quran, Surah Al-A’raf, verse 187)