Halakhah su Levitico 19:15

But this din is subject to various qualifications, as I shall explain. For if he [the object of the lashon hara] were a "mediocre" person, a plain man of Israel, who generally guarded himself against sin, and "stumbled" in this sin only occasionally, and it is possible to assume that he committed this sin unintentionally, or that he did not know this thing to be forbidden, or that he thought the ruling to be a stringent one [chumra], or conducing to a good trait in general, which saintly men are circumspect in — then, even if he saw him transgress this several times, he should certainly be given the benefit of the doubt, and it is forbidden to expose him, so that he not be an object of shame before his people, and so that he not be shamed even in his own eyes. And it is forbidden to hate him for this, for he must be judged in the scales of merit, this being a positive commandment of the Torah, according to many poskim, viz. (Vayikra 19:15): "In [the scales of] righteousness shall you judge your friend."

And if he suffered a business loss and did not know its cause, as when he held a lease from a landowner and was dismissed by him, and he did not know whether someone had slandered him or whether the landowner had dismissed him at his own initiative — it is forbidden to suspect a Jew (unless there are "indications" pointing to him [as will be explained below], in which instance he is permitted to believe the rechiluth in his heart; but he is not permitted to cause him [the suspect] any loss thereby [as will be explained below].) For it is forbidden to categorize a Jew as an "evildoer." And concerning this it is said (Vayikra 19:15): "In [the scales of] righteousness shall you judge your fellow."

(3) And sometimes he also transgresses (Vayikra 19:15): "In righteousness shall you judge your neighbor." For example, if one sees his friend saying something or doing something, which may be perceived as righteous and meritorious or as the reverse, even if he [his friend] is a mediocre person, we are obligated by the Torah in this positive commandment to judge him in the scales of merit. (And if that man is G–d-fearing, we are obligated to judge him in the scales of merit even if they incline more to guilt than to merit.) And one who goes and speaks demeaningly of him because of this thing that he said or that he did, or the receiver [of these words], who perceives him negatively because of what he has heard about him, and does not judge him in the scales of merit, transgresses this positive commandment.