Numbers 19:9,10,17
And a man that is clean shall gather up the ashes of the heifer, and lay them up without the camp in a clean place, and it shall be kept for the congregation of the children of Israel for a water of separation: it is a purification for sin.
Nave's Topical Index—AKJV

Hebrews 9:13
For if the blood of bulls and of goats, and the ashes of an heifer sprinkling the unclean, sanctifies to the purifying of the flesh:
Nave's Topical Index—AKJV