wear sackcloth and ashes

wear sackcloth and ashes -- посыпать голову пеплом
The Hebrew custom of wearing coarse and uncomfortable sackcloth and sprinkling ashes on the head, as a sign of penitence or grief or as appropriately abject attire at certain religious ceremonies, is frequently referred to in the Bible and is alluded to in the name of Ash Wednesday. Modern use of the expression, which became well known from scripture, is of course metaphorical.

see also [рвать волосы на голове]