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The Imam after me is my son, Muhammad, and after him his son `Ali, and after Ali his son, Hassan, and after Hassan his son Hujjatu’l Qa’im, 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 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 `Ali, that it was asked of the Holy Prophet, `Oh Prophet of God, when will the “support” (al-Qa’im) who is from thy family appear?’ He said, `His case is like that of the Hour (of the Resurrection). He alone will manifest it at its proper time. It is heavy in the heavens and the earth. It cometh not to you save unawares (Qur’an, 7:187).’ “
Imam Ali al Ridha (as)