signs, symptoms and cures of the spiritual diseases of the heart
Imam Mawlu̅d speaks of something that is very easy to have but is harmful to brotherhood and injurious to one's own spiritual growth. It is having a bad opinion about others, baseless assumptions, and suspicion (ẓann). This is allowing conjecture into one's heart without having any facts, which is especially harmful when one harbors a bad opinion about people who are outwardly righteous in appearance, which was something that the early Muslims considered important.
Fira̅sah
Fira̅sah is having the intuitive ability to see in people signs of goodness or evil. The Prophet ﷺ had this ability to the utmost degree and said that believers possess it also, but to a lesser extent. Sı̅dı̅ Aḥmad Zarru̅q said that every believer has the power of fira̅sah to variant degrees based on the strength of his or her faith.
Reasonable doubts
Imam Mawlu̅d says next that having doubts about someone's character is not forbidden if it is based on reason and observable evidence. This is different from suspicion that tends to be judgmental and, oftentimes, specious.
Good opinion
Having doubts about people is different from decidedly judging them negatively. Forming a bad opinion in the presence of ample evidence is common sense. However, when people repent, they should not have their past held against them. According to sacred law, people are innocent until proven guilty. This relates to having a good opinion of God.
Having a bad opinion of someone without cause is considered a malady of the heart. Often associated with this disease is backbiting (ghı̅bah), that is, speaking ill of another person behind his or her back. It is possible to backbite in an unspoken form, as when a person has unfounded negative thoughts against another person. Suspicion in the heart that affects one's thoughts and opinion of another person is considered backbiting of the heart (ghı̅bat al-qalb). This also is not permissible.
Scholars have advised that one should even beware of forming conclusions based on the bad appearance of people, for it could be that God veiled their goodness from others.
If someone says to you that a given person is bad, ask for proof. Without proof, it is tantamount to a lie. The sacred law of Islam (shariah) is based on proof and not conjecture.
If someone known to openly indulge in major sins comes with some news, one should not accept it without circumspection. One should test someone's sincerity and trustworthiness before entrusting him with anything significant (Sı̅dı̅ Aḥmad Zarru̅q). If there is much corruption in a given generation, it is best to be wary of people until their goodness becomes manifest. This is the advise of the scholars.
Scholars also say that one should be circumspect with the dispensation of zakat. In times in which goodness prevails over corruption, the default is to accept the word of people who claim they qualify for zakat and ask for it. However, when corruption and fraud are prevalent, then those responsible are obliged to be rigorous in their investigation. Charity is considered a trust from God, and its dispensation must be done with care.
"O you who believe, avoid suspicion, for some suspicion is sinful" (QUR'AN, 49:12).
"O you who believe, if an ungodly person brings you some news, then seek out its veracity" (QUR'AN, 49:6).
"Do not trust anyone with matters related to your religion, your family, or your wealth until you have tested him at least a thousand times" (Sı̅dı̅ Aḥmad Zarru̅q).
"There are two things no believer has been given anything better than: a good opinion of God and a good opinion of the servant of God" (A hadith).
A hadith states that God says, "I am in the opinion of My servant. If he thinks well of Me, he finds good, and if he thinks ill of Me, he finds evil."
"If [someone] finds good, let him thank God, and whoever finds other than that, let him blame only his own soul" (A hadith).
"Beware of a bad opinion, for it is the most false of speech" (The Prophet ﷺ).