וְכִֽי־יִהְיֶ֨ה ב֜וֹ מ֗וּם פִּסֵּ֙חַ֙ א֣וֹ עִוֵּ֔ר כֹּ֖ל מ֣וּם רָ֑ע לֹ֣א תִזְבָּחֶ֔נּוּ לַיהוָ֖ה אֱלֹהֶֽיךָ׃
And if there be any blemish therein, lameness, or blindness, any ill blemish whatsoever, thou shalt not sacrifice it unto the LORD thy God.
Mishnah Eduyot
Rabbi Hanina, chief of the priests, said: “All my days I never saw a hide taken out to the place of burning.” Rabbi Akiba said: “From his words we infer that whoever flays the hide of the firstborn beast and it is found to be trefah, the priests may enjoy the use of the hide.” But the Sages say: “[A testimony which consists of] ‘we didn’t see’ is not a proof; rather the hide must be taken out to the place of burning.