Sackcloth

Sackcloth (Hebrew: שַׂק śaq) is a coarsely woven fabric, usually made of goat's hair.

[2][3] Hessian sackcloth or burlap is not the intended biblical meaning, according to a number of scholarly sources: but the identification represents a common misconception based on phonetic association.

[6] Sackcloth came to mean a garment, too, made from such cloth, which was worn as a token of mourning by the Israelites.

Schwally based his opinion on the fact that the word "ḥagar" חָגַר (to gird)[12] is used in describing the putting on of the garment (see Joshua 1:8; Isaiah 3:24, 15:8, 22:12; Jeremiah 6:26, 49:3).

[13] Thus Schwally points to the circumstance that the Muslim pilgrim, as soon as he puts his foot on Ḥaram, the holy soil, takes off all the clothes he is wearing, and dons the iḥram.