Mishnayos Kesuvos Perek 13 Mishnah 9

With regard to two people who each produced a promissory note of a monetary debt against the other, Admon says: The one holding the note with the later date can say to the first: If I owed you money, how is it that you are borrowing from me? You should have sued to collect your debt. This is proof that your document is a forgery. And the Rabbis say: This one collects his promissory note, and that one collects his promissory note.

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: