Sefer Chofetz Chaim chapter 7 halacha 10

Another indication that lashon hara is true is circumstantial evidence, divarim nikarim, it definitely makes the lashon hara compellingly true however if it’s possible to judge the person talked about or the situation favorably then you should and not come to conclusions immediately even if there seems to be clear guilty evidence like video footage etc. The Chofetz Chaim says in a note that you should first investigate 7 times before drawing conclusions even If it seems true because the yetzer hara is very strong and quick to try to ensnare you in the trap of accepting lashon hara. No matter how clear and obvious the evidence looks, still be very diligent, 7 times, before deciding what you heard is true. After investigating if you still think it’s true then it can be accepted as truth and fact if there is no other way to judge it favorably. 

The source for this permissibility to accept lashon hara with circumstantial evidence is based on a gemara in Shabbos 56a which discusses the episode of King David supposedly accepting lashon hara from Tziva about Mefiboshes the son of Shaul that he is rebelling against the king. King David told Tziva you can have his possessions, indicating he’s accepting what Tziva said and will punish Mefiboshes. Rav said King David accepted lashon hara but Shmuel said there was indications that Tziva was right. What were the indications? That when Mefiboshes went out to greet King David later he was untidy and dishonorable looking to be in the king’s presense. Though this was a reason to suspect that what Tziva said was true but Mefiboshes rebuffed and pretended to. E friendly so King David told him to split his possessions equally with Tziva. Rav said King David accepted lashon hara because the evidence of Mefiboshes rebelling came after Tziva spoke to King David. How can King David act then upon it? The Chofetz Chaim answered that there was slight evidence that he was rebelling when he did not show up with Tziva upon King David’s request. It was only totally clear afterwards when Mefiboshes came out to greet King David in a disrespectful way. Shmuel held that King David was allowed to accept the lashon hara early because he was sure the real evidence will soon surface as it did but Rav felt that because it didn’t happen yet, the semi evidence isn’t enough and he should not have accepted it. What confounds the issue is that the gemara points out that Tziva is a proven liar in the past so even If there is partial evidence that he’s correct he lost his believability and King David should not have believed him. The Chofetz Chaim in another note said that there was other evidence that Mefiboshes was rebelling because normally he was like part of the family at King David’s table for meals and he had not shown up. This would have been evidence alone that Tziva was right if not for the fact that he proved himself to be a liar. This is why Rav said King David should not have believed him. However Shmuel held that King David listened and acted on Tziva’s advice on condition that he was correct and later saw the circumstantial evidence with his own eyes and that is why it was ok for King David to accept what he heard. What we learn from here is that without real circumstantial evidence it’s forbidden to believe someone speaking lashon hara even if he is not a proven liar until now but with circumstantial evidence even if he did lie some other time it’s permissible to believe him now.