Is one sinful for thinking ill of a person of bad character who is far from obedience to his Lord, especially if his past actions invite suspicion?

Al-Ghazali believes that ill-suspicion of Muslims is one of the gates to perdition, and it is forbidden, just like ill-speech. It refers to the heart's resolve on evil, not mere thoughts. Allah has forbidden much suspicion, saying: "O YOU WHO HAVE BELIEVED, AVOID MUCH [NEGATIVE] ASSUMPTION. INDEED SOME ASSUMPTION IS SINFUL." The reason for this prohibition is that only Allah knows the secrets of hearts, and it is not permissible to believe in evil unless it is revealed by an undeniable observation. One must disbelieve Satan if he casts evil into the heart, and verify the news from an evildoer. Among the dangers of ill-suspicion are that it leads to backbiting, neglecting the rights of Muslims, contempt, and self-admiration. The Prophet (peace and blessings be upon him) warned against exposing oneself to accusation. Good suspicion of a believer is required, but good suspicion is not extended to people of evil and wickedness.