'Sackcloth' in the Bible

Thou hast turned for me my mourning into dancing; Thou hast loosed my sackcloth, and girded me with gladness;

But as for me, when they were sick, my clothing was sackcloth: I afflicted my soul with fasting; And my prayer returned into mine own bosom.

When I made sackcloth my clothing, I became a byword unto them.