Mishnah
The Mishnah, the central compilation of Rabbinic Oral Law, contains a tractate on the Red Heifer, Tractate Parah ("Cow") in Seder Taharot, which explains the procedures involved. The tractate has no existing Gemara, although commentary on key elements of the procedure is found in the Gemarah for other tractates of the Talmud. According to Mishnah Parah, the presence of two black hairs invalidates a Red Heifer, in addition to the usual requirements of an unblemished animal for sacrifice.
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