'Sackcloth and Ashes' in the Bible

In each and every province that the decree and law of the king reached, there was great mourning among the Jews, with fasting, weeping and wailing; and many lay on sackcloth and ashes.

“Is a fast such as this what I have chosen, a day for a man to humble himself [with sorrow in his soul]?Is it only to bow down his head like a reedAnd to make sackcloth and ashes as a bed [pretending to have a repentant heart]?Do you call this a fast and a day pleasing to the Lord?

So I directed my attention to the Lord God to seek Him by prayer and supplications, with fasting, sackcloth and ashes.