英文谚语:一言既出，驷马难追

 A word spoken is past recalling.

　　一言既出，驷马难追

　　Explanation: the harm done by a careless word can not easily undo.

　　Example: for the rest of his life he regretted what he had said, but a word spoken is past recalling and he knew he could never repair the damage of that moment of harshness.