'Sackcloth' in the Bible

It happened that when the king heard the words of the woman, he tore his clothes. Now he had been walking on the wall, and the people saw, and behold, sackcloth was over his flesh underneath.

It happened that when King Hezekiah heard, he tore his clothes and covered himself with sackcloth and went [to] the temple of Yahweh.

He sent Eliakim who [was] over the palace, Shebna the secretary, the elders, and the priests, [all] clothed in sackcloth, to Isaiah the prophet the son of Amoz.