Yoreh Deah Siman 16 Seif 12

 

יב בְּהֵמָה שֶׁנִּשְׁחֲטָה אִמָּהּ אוֹ בִּתָּהּ הַיּוֹם וְנִתְעָרְבָה בַּאֲחֵרוֹת וְצָרִיךְ לִשְׁחֹט מֵהֶם הַיּוֹם, כֵּיצַד תַּקָּנָתוֹ, נִכְבְּשִׁינְהוּ, דְּנַיְדֵי מִמְּקוֹם קְבִיעוּתָן, וְיִקַּח מֵהֶם אֶחָד וְיִשְׁחֹט, דְּכָל דְּפָרִישׁ מֵרֻבָּא פָּרִישׁ; וּשְׁנַיִם הַנּוֹתָרִים אָסוּר לְשָׁחֲטָם הַיּוֹם.

 

Seif 12

An animal that is slaughtered whether it is a mother or its offspring on that day and they get mixed together and the other one needs to be slaughtered the same day, what do we do?

We slaughter one by one until two are left which cannot be slaughtered the same day because whatever is removed from a group is part of the majority which these two are not slaughtered on the same day.