Red heifer

The Red Heifer (Hebrew: פרה אדומה‎; Parah Adumah), also known as the red cow, was a cow brought to the priests as a sacrifice according to the Hebrew Bible, and its ashes were used for the ritual purification of Ṭum'at HaMet ("the impurity of the dead"), that is, an Israelite who had come into contact with a corpse.

Hebrew Bible (Torah)

Book of Numbers

According to Numbers 19:2: "Speak unto the children of Israel, that they bring thee a red heifer without spot, wherein is no blemish, and upon which never came yoke".

The Book of Numbers stipulates that the cow must be red in color, without blemish, and it must not have been used to perform work (Numbers 19:2). The heifer is then ritually slaughtered (Numbers 19:3) and burned outside of the camp (Numbers 19:3–6). Cedar wood, hyssop, and wool or yarn dyed scarlet are added to the fire, and the remaining ashes are placed in a vessel containing pure water (Numbers 19:9).

In order to purify a person who has become ritually contaminated by contact with a corpse, water from the vessel is sprinkled on him, using a bunch of hyssop, on the third and seventh day of the purification process (Numbers 19:18–19).