Kesuvos2: 3
הָעֵדִים שֶׁאָמְרוּ: ,,כְּתַב יָדֵינוּ הוּא זֶה, אֲבָל אֲנוּסִים הָיִינוּ”, ,,קְטַנִּים הָיִינוּ”, ,,פְּסוּלֵי עֵדוּת הָיִינוּ” — הֲרֵי אֵלּוּ נֶאֱמָנִים. וְאִם יֵשׁ עֵדִים שֶׁהוּא כְתַב יָדָם, אוֹ שֶׁהָיָה כְתַב יָדָם יוֹצֵא מִמָּקוֹם אַחֵר — אֵינָן נֶאֱמָנִין.
[If] witnesses said: “This is our handwriting, but we were coerced,” [or] “we were minors,” [or] “we were unfit for testimony,” these are believed. If, however, there are witnesses that it is their handwriting, or if their handwriting is verified from another source, they are not believed.