What is the ruling on insulting the four imams out of ignorance?

Reviling Muslims in general is considered an act of transgression (fisq). Its ugliness and magnitude of sin increase when directed towards Muslim scholars, as reviling them is among the major sins. This is because they possess an additional right to veneration and exaltation. Jurists have explicitly stated that slandering people of knowledge is a major sin, and whoever reviles the scholars of the Pious Predecessors (Salaf as-Salih) has deviated from the straight path. Furthermore, reviling a scholar harms the knowledge they carry and diminishes their standing in the eyes of the people, which in turn harms the Shari'ah. Therefore, repentance for reviling them is obligatory.