Behar al-Anwar, Volume 51

According to Fiqh E Jaferia..... To know the Imam of The Time is one of the Prophetic injunctions to all mankind accepted unanimously across the different schools of thought. Imam Mahdi AFS, The Twelfth Imam after The Prophet SAWW , is our Imam of the Time. 
Allamah Majlisis book is divided into xxv chapters with prefatory matter and appendices that take the reader through from the Imam AS birth, lineage, names and titles and ahadith foretelling his birth and advent to the period of his ghaibah, both the short (al-ghybah al-sughra) and long (al-ghaybah al-kubra), his deputies (emissaries) reappearance and rule, impostors who laid claim to being the emissaries and gateways to the Imam AS, the holy letter from The Imam AS about Muhammad Ibn Ali al-Shalmaghanis blasphemous claims and falsehood. The translator of Allamah Majlisis book has incorporated the original Arabic narrations that are culled from a wide variety of sources, inter alia, Nahjul Balaghah, Al-Kafi, Al-Ghaiba of Sheikh Tusi, Ikmal al-Din, Al- Ghaibah of Al-Numani rendering the book rich in its content. 
His sources are not confined to the Shia texts only; rather, he also quotes Sunni texts, which testifies to the authenticity of the presence of The Imam AS in Ghaibah. Abdullah ibn Umar, for example is quoting The Prophet SAWW The Mahdi will rise and there will be a cloud over his head, from which a caller will be calling: This is the Mahdi, the Caliph of Allah. One of the rare veritable ahadith from Abu Huraira is also quoted: The Hour shall not rise until a man from my Household reigns. He will conquer Constantinople and the Mount of Dailam. If there should remain but no more than one day, Allah will prolong that day.