'Sackcloth' in the Bible

“Woe (judgment is coming) to you, Chorazin! Woe to you, Bethsaida! For if the miracles done in you had been done in Tyre and Sidon [cities of the Gentiles], they would have repented long ago in sackcloth and ashes [their hearts would have been changed and they would have expressed sorrow for their sin and rebellion against God].

“Woe (judgment is coming) to you, Chorazin! Woe to you, Bethsaida! For if the miracles performed in you had been performed in Tyre and Sidon, they would have repented and changed their minds long ago, sitting in sackcloth and ashes [to show deep regret for sin].

I looked when He (the Lamb) broke open the sixth seal, and there was a great earthquake; and the sun became black as sackcloth [made] of hair, and the whole moon became like blood;

And I will grant authority to My two witnesses, and they will prophesy for twelve hundred and sixty days (forty-two months; three and one-half years), dressed in sackcloth.”