How can one avoid having ill thoughts about people, especially Muslims, and is it always necessary to think well of others, despite being surprised by the actions of some Muslims that contradict the creed and raise suspicion about people's actions?

A Muslim should not be preoccupied with monitoring people and seeking out their faults. Rather, he should focus on reforming himself, as this preoccupation keeps him from thinking ill of others. The Prophet Muhammad (peace be upon him) forbade seeking out the faults of Muslims, because it leads to arrogance and ill thoughts about people. It is forbidden to think ill of a Muslim unless there is clear, decisive evidence and manifest proof, in which case the necessity is weighed accordingly. The obsession with thinking ill of others can be treated by occupying oneself with one's own faults, by recalling the religious texts, and by looking at the positive aspects of people. When an evil thought enters the heart, one must disbelieve Satan and increase in honoring the person about whom one harbored ill thoughts. If a Muslim's slip-up is confirmed, then the advice should be given secretly and with a sorrowful heart.