'Sackcloth and Ashes' in the Bible

And in every province, whithersoever the king's commandment and his decree came, there was great mourning among the Jews, and fasting, and weeping, and wailing; and many lay in sackcloth and ashes.

Is such the fast that I have chosen? the day for a man to afflict his soul? Is it to bow down his head as a rush, and to spread sackcloth and ashes under him? wilt thou call this a fast, and an acceptable day to Jehovah?

And I set my face unto the Lord God, to seek by prayer and supplications, with fasting and sackcloth and ashes.