In his book “Sharhul Ziyaratul Jamiyah” p 150, known and respected shia scholar said:

[ وقد دلت أخبار كثيرة على كفر المخالفين يحتاج جمعها إلى كتاب مفرد]

Translation:

And a lot of narrations shows to disbelief of opposition (1), (so much narrations) that there is a need in gathering them all in independent book.

1) Mean those who opposes truth in shia understanding.