בכורות ו׳Bechorot 6

Passage 1א׳

בכורות פרק ו - [פִּסְקָא] אֵיזֶהוּ תַּבְלוּל? לָבָן הַפּוֹסֵק אֶת הַסִּירָה וְכוּ'. רַבִּי יוֹסֵי אוֹמֵר: לָבָן נִכְנָס בַּשָּׁחוֹר, הֲרֵי זֶה מוּם. שָׁחוֹר וְנִכְנָס בַּלָּבָן, אֵינוֹ מוּם, שֶׁאֵין מוּמִין בַּלָּבָן. אָמַר רַב: מַאי טַעְמָא דְּרַבִּי יוֹסֵי? דִּכְתִיב: (תהילים ע״ג:ז׳) "יָצָא מֵחֵלֶב עֵינֵימוֹ", "תַּרְבָּא דְּעֵינָא" אִיקְרִי, "עֵינֵימוֹ" סְתָמָא לָא אִיקְרִי.

"Which is the tevalul? A white that breaks through the ring": Whose is our mishnah? It is Rabbi Yose's. For it was taught: white that enters into the black, or black that enters into the white — this is a blemish; the words of Rabbi Meir. Rabbi Yose says: white that enters into the black, this is a blemish; black that enters into the white is not a blemish, for there are no blemishes in the white. Rav said: what is the reason of Rabbi Yose? For it is written "their eye stands out from fatness" (Psalms 73:7) — the white of the eye is called the fat of the eye, but "the eye" without qualification it is not called. And Rabbi Meir, what is his reason? What is the sense of the word tevalul? A thing that confuses the eyes.

our rendering of Bechorot 38b