And a pure man shall gather the ashes of the heifer and place them outside the camp in a pure place; and it shall be for the congregation of the children of Yisrael for a keeping, for water of sprinkling; it is a chatas.
Torah Temimah: Avodah Zarah 23b — A para that was raped is invalid. Why? The Merciful One called it a “chatas.”
English: A para that was raped is invalid. Why? The Merciful One called it a “chatas.”
Analogy from the designation “chatas.”
Because the Torah calls the para a “chatas,” the same disqualifications that apply to a chatas offering (including sexual use) apply to the para aduma as well.