Ihtijaaj:  It is narrated  from Abu Hamza  Thumali  from Abu Khalid Kabuli from Ali bin Husain (a.s.) that he said:

“O Abu Khalid, the  twelfth  successor  [Mahdi] of  the  Messenger   of  Allah (s.a.w.s.) will have a long occultation.  O Abu Khalid, those who live in his [Mahdi’s] Imamate during his [Mahdi’s] occultation would be waiting from his reappearance. They will be superior to the people of every age. Because the Almighty Allah will bestow them [companions of Mahdi] with such understanding and recognition that for them the occultation will be like presence… They will be sincere people. They will be propagating the religion of Allah, openly and discreetly.”

[The Promised Mahdi, Allamah Muhammad Baqir al-Majlisi, Biharul Anwar, Volume 13 (Old Edition)/Volumes 51-52-53 (New Edition)]