וַיִּקְרָ֨א אֱלֹהִ֤ים ׀ לָאוֹר֙ י֔וֹם וְלַחֹ֖שֶׁךְ קָ֣רָא לָ֑יְלָה וַֽיְהִי־עֶ֥רֶב וַֽיְהִי־בֹ֖קֶר י֥וֹם אֶחָֽד׃ (פ)
빛을 낮이라 칭하시고 어두움을 밤이라 칭하시니라 저녁이 되며 아침이 되니 이는 첫째 날이니라
Mishnah Chullin
The “one day” mentioned in connection with the law of “it and its young” means the day and the night preceding it. This was how Rabbi Shimon ben Zoma expounded (darash): it says “one day” (Genesis 1:5) in connection with the creation and it also says “one day” (Leviticus 22:28) in connection with “it and its young” Just as the “one day” mentioned in connection with the creation means the day and the night preceding it, so too the “one day” mentioned in connection with “it and its young” means the day and the night preceding it.