Censure of Disbelief in Imam Mahdi (A.S.)
 
The Holy Prophet (S.A.W.S.) said,

"One who disbelieves in the Qaem from my sons, disbelieves in me."
(Kamaaluddin Vol.2 Pg.412) 
The Holy Prophet (S.A.W.S.) said,
"The Qaem is from my Progeny (sons). His name is my name. And his kunniyat (agnomen) is my kunniyat. And his appearance is (like) my appearance. And his behaviour is (like) my behaviour. He will establish among the people my practice and my shariat. And he will call them towards the book of his Lord, the High and the Mighty. One who obeys him has obeyed me. And one who denies his 'ghaibat' has denied me." 
(Kamaaluddin Vol.2. Pg.411)

Imam Jafar as Sadiq (A.S.) said:
"One who believes in all Imams (A.S.) from my forefathers and my sons, but denies Al Mahdi from my sons. He is like the one who believes in all the Prophets and denies Muhammad, sallallaho Alaihe wa Aalehi." 
(Kamaaluddin Vol.2. Pg. 338 and 411)