A word spoken is past recalling

Once you have said a thing, it is too late to regret having said it. We find the following in The Rubaiyat of Omar Khayyam translated by Edward FitzGerald:

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.

See also:

• What's done cannot be undone