'Sackcloth' in the Bible

Then David said to Joab and to all the people who were with him, “Tear your clothes and gird on sackcloth and lament before Abner.” And King David walked behind the bier.

And Rizpah the daughter of Aiah took sackcloth and spread it for herself on the rock, from the beginning of harvest until it rained on them from the sky; and she allowed neither the birds of the sky to rest on them by day nor the beasts of the field by night.