'Sackcloth' in the Bible

When the king heard the words of the woman, he tore his clothes—now he was passing by on the wall—and the people looked, and behold, he had sackcloth beneath on his body.

And when King Hezekiah heard it, he tore his clothes, covered himself with sackcloth and entered the house of the Lord.

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