Salam alaykum.

Book “Fiqh” Kitab at-tahara, author Ayatollat Sayed Muhammad Shirazi. Darul Ulum, Lebanon.

“As for all the other groups [sects] of the shia – other than the the itnaa ashariyya [The twelvers] : then many texts have proved their disbelief , like the previous narrations which have been mentioned. They prove that ”Whoever denies [rejects / opposes] an Imam : is like one who said : ‘Allaah is one of three.’ “