Sefer Chofetz Chaim Chapter 3 footnote 10

We concluded the unit on judging your fellow Jew favorably. The Chofetz Chaim said that even though it is very proper and good character to judge one favorably in cases when it would seem more unfavorable, however technically according to halacha one does not have to judge favorably in this circumstance. But if one does judge others favorably even in these circumstances, at least treating it as a doubt them Hashem will reciprocate and judge you favorably.

Two cases in the Gemara where they did not judge favorably but the reason being is because halachically you don’t need to and these were extenuating circumstances which was not worth going beyond the letter of the law:

1. Bava Metzia 75b: There is a halacha that one should not lend money without witnesses lest the would be borrower would deny he borrowed money and people will curse the lender for giving a bad name to the would be borrower for no reason. This was a real issue to the point that Ravina would not lend money to Rav Ashi without witnesses, lest he forgot he borrowed money, even though they were partners together in writing down the Gemara and they were the leading rabbis of their generation. Why didn’t people judge the lender favorably and not curse him if he claimed the borrower owes him money, maybe he is correct? It must be that halachically one can judge others unfavorably in situations like this where there should have been witnesses at the time of the loan.

2. Sanhedrin 26a: Rebbe Chiya bar Zarnuki and Rebbe Shimon ben Yehotzadak were on there way to the Sanhedrin to testify that there should be a leap year that year. That year happened to be a shmita (sabbatical) year and they saw people in the field plowing and assumed they were hired to plow in a non-Jewish owned field. They then saw people tending to a vineyard and assumed they were fixing fences not working on the actual crop. Reish Lakish saw these two rabbis did not reprimand either of these people and thought they should not be allowed to testify because they don’t care about the laws of shmita so they did not reprimand those people in the fields. He even told Rebbe Yochanan not to accept them as witnesses. Why didn’t Reish Lakish judge them favorably, especially since they were such great sages, Amoraim! It must be that he had no obligation to, and because these farmers looked like they were doing something wrong, and transgressing shmita is so severe than Reish Lakish felt he should not go beyond the letter of the law but rather according to strict judgment and assume there was a problem.

3. On the other hand we see the opposite illustration in Shabbos 127b where a worker judged his employer favorably when the worker asked for his salary right before Yom Kippur and the employer said he had no money, land, possessions or even food that he can send back home with him. The employer then came to him after Sukkos, paid him plus gave him a bonus and asked his employee what he was thinking. When the employee gave excuses, judging his employer favorably with some far fetched excuses, the employer said all that is pretty much true and just as you judged me favorably so should Hashem judge you favorably.