Numbers 19:5Hebrews 9:13

To cover the head with ashes was a token of self-abhorrence and humiliation (2 Samuel 13:19; Esther 4:3; Jeremiah 6:26 , etc.).

To feed on ashes (Isaiah 44:20 ), means to seek that which will prove to be vain and unsatisfactory, and hence it denotes the unsatisfactory nature of idol-worship. (Compare Hosea 12:1 ).