What is the cure for having ill thoughts about others, and what is the meaning of "And if you have a thought [about someone], do not pursue it [to verify]," and is this a sound hadith?

Ill-opinion (su' adh-dhann) is when you do not interpret your Muslim brother’s action in a negative way, so long as it can be interpreted positively. It is considered one of the inward major sins. Its remedy lies in repelling it from the self and affirming that a Muslim’s true state is hidden from you, and that what you have seen from him could be either good or bad. The sign of a deep-seated suspicion manifests in a change of heart through aversion and a feeling of burden, as well as a cooling off from showing respect and honor. It was said: "If you suspect, do not verify," meaning do not confirm the suspicion within yourself through word or deed. For Satan may cast the faults of people before a person to make him believe them to be shrewdness and light, when in reality they are the delusion and darkness of devils.