"the fickle finger of fate"

.

The moving finger writes and having writ
Moves on; nor all your piety nor wit
Shall lure it back to cancel half a line,
Nor all your tears blot out a word of it.

-- From The Rubaiyat of Omar Kayyam 

This, I imagine, is the source and inspiration for the malaprop, yet 

perfectly descriptive, "fickle finger of fate."

.