Some migrant-companions are narrated to have told Imam Mahdi Ahs "We will remain near your mausoleum after you."
The Imam Ahs said "Open my grave and see. If I (my body) am there (in the grave), I am not the Mahdi. As long as our aim and scope (that is, the Vision of Allah) remains among you. This servant will be among you, wherever you are."
(Hashia Insaaf Nama - Hashia Sharif, N.77)