וַיִּֽקַּֽח־ל֣וֹ חֶ֔רֶשׂ לְהִתְגָּרֵ֖ד בּ֑וֹ וְה֖וּא יֹשֵׁ֥ב בְּתוֹךְ־הָאֵֽפֶר׃
And he took him a potsherd to scrape himself therewith; and he sat among the ashes.
Read Kabbalistic (mystical) interpretations of Job 2:8: Zohar and classical Jewish mystical sources, free online.