'Sackcloth' in the Bible

And David saith unto Joab, and unto all the people who are with him, 'Rend your garments, and gird on sackcloth, and mourn before Abner;' and king David is going after the bier.

And Rizpah daughter of Aiah taketh the sackcloth, and stretcheth it out for herself on the rock, from the commencement of harvest till water hath been poured out upon them from the heavens, and hath not suffered a fowl of the heavens to rest upon them by day, or the beast of the field by night.