Abd al-Aziz ibn Muslim narrated:
"His [Imam Mahdi (pbuh)'s] knowledge is sophisticated and his forbearance is absolute. He is profound in imamate (leadership) and wise in politics. It is a religious obligation to obey him [Mahdi (pbuh)]. He was assigned to this position by the will of God Azza wa-Jalla. He [Mahdi (pbuh)] counsels the servants of God. He is the protector of the religion of God."
(Book of Belief and Blasphemy, Usul al-Kafi (Al-Usul min Al-Kafi), Al-Kulayni, Volume 1, page 280)