The Shi'is are fanatical, ignorant and worse and they have strayed far from the pure faith of Islam.

He (Baha'u'llah) calls into question the legitimacy of the doctrines of the vast majority of Muslims who do not follow the twelve Imams and who are called Sunnis. Hence, he depicts Islam as getting off to a bad start and then continuing to deviate from the intentions of the prophet Muhammad. Baha’u’llah denies that the twelfth Imam was a real person and affirms rather his symbolic existence in the minds of Shi’is. He calls Shi’is fanatical and ignorant and worse. So while they recognized the Imams, since their line came to an end, they have strayed far from the pure faith of Islam.

http://bahai-library.com/terry_bahaullah_reconciliation_religions