'Sackcloth' in the Bible

David instructed Joab and all the people who were with him, "Tear your clothes! Put on sackcloth! Lament before Abner!" Now King David followed behind the funeral bier.

Rizpah the daughter of Aiah took sackcloth and spread it out for herself on a rock. From the beginning of the harvest until the rain fell on them, she did not allow the birds of the air to feed on them by day, nor the wild animals by night.