Numbers 19:9; Numbers 19:17

9 Then someone who is ritually clean is to collect the ashes of the cow and put them in a ritually clean place outside the camp, where they are to be kept for the Israelite community to use in preparing the water for removing ritual uncleanness. This ritual is performed to remove sin.

17 To remove the uncleanness, some ashes from the red cow which was burned to remove sin shall be taken and put in a pot, and fresh water added.