It is narrated from the Prophet of Islam (PBUH) who said:

How prosperous is the one who realizes/recognizes the Qaem (Imam Mahdi (AJ)) of my Ahlul Bait (AS) whilst being his follower before the uprising, and be among the followers of Welayah, and friends of Hadhrat (Mahdi (AJ)). And be against the enemies of Imam (Mahdi (AJ)), Welayah, and the guiding leaders before his re-appearance. These people (the followers of Imam Mahdi (AJ)) are my companions and friends, and they are very dear to me {1].

[1] Al-Qeebah, Sheikh Toosi, Vol. 1, Page 456; Beharul Anwaar, Vol. 52, Page 129.

Source: en.shafaqna.com