Yoreh Deah Siman 18 Seif 13

 

יג

שָׁחַט בְּסַכִּין בָּדוּק, וְנֶאֱבַד קֹדֶם שֶׁיִּבְדְּקֶנּוּ, אַחַר שְׁחִיטָה, וְאַחַר כָּךְ נִמְצָא וְהוּא פָּגוּם, שְׁחִיטָתוֹ כְּשֵׁרָה הוֹאִיל וְיָצָא בְּהֶתֵּר, וְזֶה שֶׁנִמְצָא פָּגוּם אֵמוּר שִׁבֵּר בָּהּ עֲצָמוֹת וְלָאו אַדַּעְתֵּהּ, דְּאוֹקֵי סַכִּין אַחֶזְקָתֵהּ

 

Seif 13

 

If one slaughters with a knife that was checked, and checked before and the knife was lost before it was checked after the slaughter, and afterwards we find the knife and see it flawed, the slaughter is acceptable inasmuch as it performed properly. And if we find a flaw as stated that smashed a bone without knowing after the slaughter, and the knife remains with the established chazaka.