Along with goats' and bulls' blood, Hebrews 9:13 mentions the sprinkled ashes of what animal?

Answer: A heifer

The blood of goats and bulls and the ashes of a heifer sanctified the unclean outwardly; how much more will Christ's blood cleanse.

“For if the blood of goats and bulls and the ashes of a heifer sprinkled on those who are ceremonially unclean sanctify them so that their bodies are clean,”— Hebrews 9:13 (BSB)