What is the poem The moving finger writes?

The Moving Finger Writes is not a poem but a quotation from a famous poem. It is a stanza, a Quartrain from Omar Khayyam's The Rubaiyat, as translated by Edward Fitzgerald: The moving finger writes, and having writ Moves on, nor all your piety or wit Shall lure it back to cancell half a line, Nor all your tears wash out a word of it.