'Sackcloth' in the Bible

And it came to pass, when the king heard the words of the woman, that he rent his clothes (now he was passing by upon the wall); and the people looked, and, behold, he had sackcloth within upon his flesh.

And it came to pass, when king Hezekiah heard it, that he rent his clothes, and covered himself with sackcloth, and went into the house of Jehovah.

And he sent Eliakim, who was over the household, and Shebna the scribe, and the elders of the priests, covered with sackcloth, unto Isaiah the prophet the son of Amoz.