Moses
Numbers 19:9ESV·traditional attribution

And a man who is clean shall gather up the ashes of the heifer and deposit them outside the camp in a clean place. And they shall be kept for the water for impurity for the congregation of the people of Israel; it is a sin offering.

Matthew Henry Presbyterian @wholebiblehenry

We have here the divine appointment concerning the solemn burning of a red heifer to ashes, and the preserving of the ashes, that of them might be made, not a beautifying, but a purifying, water, for that was the utmost the law reached to; it offered not to adorn as the gospel does, but to cleanse only.

Commenting on Numbers 19:1-10

John Gill Reformed Baptist @doctorgill

And a man that is clean shall gather up the ashes of the heifer,.... A man, a clean priest, as the Targum of Jonathan; in later times great care was taken that the priest concerned in the burning of the red cow should be pure; he was separated from his own house seven days before the time, and every day he was sprinkled with the...

Geneva Bible Notes Reformed @genevanotes

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.