Related for Gittin 108:9

[Relatedly, if the friend] was bringing a sacrifice with him, and he said to [the friend], "[This sacrifice] has become piggul," [or] if he was preparing pure food with him, and he said, "It became impure," a Jew is not suspected on these things. But [if] he said to him, "The sacrifice that I brought with you became impure on the same day," by the the letter of the law, he is not to be believed. Rabbi Yehudah says, a Jew is [typically] not suspected on these things, but everything goes according to what kind of a man he is.