The Rafidhah have absolutely nothing to do with Islam
Imam Ahmad :
They (Rafidhah) are those who disassociate themselves from the Companions of the Prophet Muhammad (peace be upon him), insulting them and disparaging them. They declare all the leaders [Companions] to be disbelievers except for four: Ali, Ammar, Al-Miqdad, and Salman. The Rafidha have absolutely nothing to do with Islam.
هم الذين يتبرأون من أصحاب النبي محمد صلى الله عليه وسلم يسبونهم وينتقصونهم ويكفرون ألأئمة إلا أربعة: علي وعمار والمقداد وسلمان وليست الرافضة من الإسلام في شيء
Source : as-Sunnah p. 82 Link