Is a Muslim obligated to have a good opinion of a disbeliever? May Allah reward you.

One is not obligated to think well of a disbeliever (kafir); rather, thinking ill of him is more appropriate than thinking ill of a Muslim who openly commits immoral acts (fasiq). It is forbidden to think ill of Allah and of a Muslim whose uprightness (adalah) is apparent. It is obligatory to think well of Allah, and commendable to think well of a Muslim. There is no harm in thinking ill of someone whose outward appearance indicates evil. The hadith, "Beware of suspicion, for suspicion is the falsest of speech," is understood to apply to mere suspicion that is not supported by any evidence.