'Sackcloth' in the Bible

It happened, when the king heard the words of the woman, that he tore his clothes (now he was passing by on the wall); and the people looked, and behold, he had sackcloth underneath on his flesh.

It happened, when king Hezekiah heard it, that he tore his clothes, and covered himself with sackcloth, and went into the house of Yahweh.

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