1؎: Mentioning the evils of deceased disbelievers (kuffar) and transgressors (fussaq), if done so that people may avoid them and take heed, is permissible. Similarly, criticism and evaluation (jarh wa ta'dil) of weak and criticized narrators of hadith is, by consensus of the scholars, permissible—whether the narrator is dead or alive—because its purpose is the service and protection of creed ('aqidah), knowledge, and hadith.
Explanation & Benefits
Shaykh Umar Farooq Saeedi
Benefits and Issues: The deceased has already departed to the next world to receive the reward or punishment for his deeds; now, mentioning his faults will only cause distress to his heirs and become a cause of mutual enmity among you. However, if there is a Shari‘ah-based necessity to clarify someone’s disbelief, polytheism, or innovation, then it should be stated so that people remain cautious—for example, if certain individuals have been the cause of spreading corrupt beliefs or have been weak in the narration of hadith, then mentioning them is a part of the religion, not due to any personal motive.
Source: Sunan Abu Dawood – Commentary by Shaykh Umar Farooq Saeedi, Page: 4900