Here you go :
►Sheykh As-Sadduq in Al i'tiqad page 78:
"And our belief about who does not believe in Imamat of the Commander of Believing Ali and other Imam after him is that it is similar to that which does not believe in the prophety (nubuwa) of all the Prophets."
►Al Majlissi in Bihar Al Anwar:
"Knows that the application of the terms shirk (polytheism) and kufr (unbeliever) against those who don't believe in Imama of the Commander of Believing (i.e Ali) and of the Imam among its descendants (i.e 11 other Imam), peace be upon them, and who place another man above them (in term of merits), are non-believers who will remain eternally in hell."
►Sheikh Al Mufid in Al Masa'il:
"There is consensus between the imamiya scholars on the fact that somebody who did not believe in Imama of one of the Imam and who did not believe in what Allah established like obligation to obey to them, that such a person is a mislaid non-believer, and which will deserve to remain eternally in hell."
►Fatwa of ayatollah Rohani who says that sunni won't go in heaven because they don't believe in the Walayat of Ali
http://www.imamrohan...opic.php?t=1861
►Nimatullah Al-Jazaeri in Al-Anwar Al-Numaniya (Vol 1 p. 278/279):
"We do not agree with Nasibis about Allah nor a prophet nor an Imam, for they say that their God is the one whose prophet is Muhammad (a.s) and his Khalifah after him is Abu Baker. We do not believe in this God nor this Prophet, because the God whose prophet's Khalifa is Abu Baker is not our God and that Prophet is not our Prophet"
"...Rejecting us(Imams) is rejecting Allah and that is up to the level of paganism and considering things equal to Allah..."
Al-Kafi, Book on Virtue of Knowledge, H 196, Ch. 21, h 9