extract from wikipedia
The book takes its name from verse 51 of Edward FitzGerald's translation of the Rubáiyát of Omar Khayyám:
The Moving Finger writes; and, having writ,
Moves on: nor all thy Piety nor Wit
Shall lure it back to cancel half a Line,
Nor all thy Tears wash out a Word of it.
The poem, in turn, refers to Belshazzar's feast as related in the Book of Daniel, which is the source of the common phrase the writing on the wall