The position of jurists concerning one who curses the Ṣaḥābah, believing that such an act is permissible, is that he has committed an act of disbelief. If he curses them but does not believe that cursing them is permissible, then he is guilty of immorality, and not disbelief.
 Imām ash-Shāfiʿī
On one occasion, ash-Shāfiʿī said concerning the Shiʿah, “I have not seen among the heretics a people more famous for falsehood than the Rāfiḍī Shiʿah.”  On another occasion he said, “Narrate knowledge from everyone you meet except the Rāfiḍī Shiʿah, because they invent Ḥadīths and adopt them as part of their religion.” 
 ʿAbdullāh Ibn al-Mubārak
Ibn al-Mubārak was reported to have said, “Religion is gained from Ahlul-Ḥadīth, scholastic theology and crafty exemptions from religious ordinances of Ahlur-Ra’yee (the people of opinion) and lies from the Rāfiḍī Shiʿah.” 
 Al-Qāḍī Abū Ya‘lā
It was reported that Abū Ya‘lā said, “The position of jurists concerning one who curses the Ṣaḥābah, believing that such an act is permissible, is that he has committed an act of disbelief. If he curses them but does not believe that cursing them is permissible, then he is guilty of immorality, and not disbelief.” 
 Ibn Hazm al-Andaloosee
One day during the period of Muslim rule in Spain, Imām Abū Muḥammad Ibn Hazm was having a debate with some Spanish Catholic priests about their religious texts. He brought before them evidence of textual distortions in the Bible and the loss of original manuscripts. When they replied by pointing out to him Shee‘ee claims also being distorted, Ibn Hazm informed them that “The Shiʿah could not be used as evidence against the Qurʾān or against Muslims because they are not themselves Muslims.” 
 Muhibbud-Dīn al-Khaṭīb
This scholar wrote a book on them called al Khutootul-‘Areedah lil-Ususūllatee Qaama ‘Alayhaa Dīnish-Shiʿah al-Ithnā ‘Ashriyyah (lit. Broad outlines of the basis for the Twelver Shee‘ee Creed). He also footnoted earlier works on the Shiʿah like Al-Muntaqaa and ‘Awaasim minal-Qawaasim. In all of his works, he considers the Shiʿah to be disbelievers.
 Related by Shaykh al-Islām Ibn Taymīyyah in Minḥājus-Sunnatin-Nabawiyyah (1/39).
 Minḥājus-Sunnatin-Nabawiyyah (p. 38).
 Related by Imām al-Dhahabī in al-Muntaqaa min Minḥājil-I‘tidaal (p. 480).
 Related by Shaykh al-Islām Ibn Taymīyyah in as-Sawaarimul-Maslool (p. 569).
 Related by Ibn Hazm in al-Fisaal fil-Milal wan-Nihaal (2/78) and (4/182).