sackcloth and ashes - Phrases/Idioms
The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Mourning or penitence, as in What I did to Julie's child was terrible, and I've been in sackcloth and ashes ever since. This term refers to the ancient Hebrew custom of indicating humility before God by wearing a coarse cloth, normally used to make sacks, and dusting oneself with ashes. In English it appeared in William Tyndale's 1526 biblical translations (Matthew 11:21), “They [the cities Tyre and Sidon] had repented long ago in sackcloth and ashes.”