From Longman Dictionary of Contemporary Englishwear sackcloth and asheswear sackcloth and ashesBritish EnglishSORRY/APOLOGIZE to behave in a way that shows everyone you are sorry about something wrong you have done → sackcloth
Examples from the Corpus
wear sackcloth and ashes• I have no wish to see Aitken go through the rest of his life wearing sackcloth and ashes. 