Pesachim 4a:12פסחים ד׳ א:י״ב
Rav Naḥman bar Yitzḥak said to them that we already learned the resolution to this dilemma based on a related baraita: Everyone is believed to provide testimony about the elimination of leavened bread; even women, even slaves, and even minors. Although these people are typically not relied upon to deliver testimony, they are believed when they provide testimony that they have eliminated leaven. The Gemara asks: What is the reason that they are believed?
Meiri on Pesachim 4a:8מאירי על פסחים ד׳ א:ח׳
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