'Sackcloth' in the Bible

And David said to Joab, and to all the people that were with him, Rend your clothes, and gird you with sackcloth, and mourn before Abner. And king David followed the bier.

And Rizpah the daughter of Aiah took sackcloth, and spread it for her upon the rock, from the beginning of harvest until water was poured upon them from heaven; and she suffered neither the birds of the heavens to rest on them by day, nor the beasts of the field by night.