Reference for Ketubot 13:9

שְׁנַיִם שֶׁהוֹצִיאוּ שְׁטָר חוֹב זֶה עַל זֶה, אַדְמוֹן אוֹמֵר, אִלּוּ הָיִיתִי חַיָּב לְךָ, כֵּיצַד אַתָּה לֹוֶה מִמֶּנִּי. וַחֲכָמִים אוֹמְרִים, זֶה גוֹבֶה שְׁטַר חוֹבוֹ וְזֶה גּוֹבֶה שְׁטַר חוֹבוֹ:

If two men presented bills of indebtedness to each other, Admon says: (The one with the bill of the later date can say:) "If I were indebted to you, how could you borrow from me?" And the sages say: This one claims his bill of indebtedness, and that one claims his bill of indebtedness. [The halachah is in accordance with the sages.]

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