一言既出， 驷马难追

一言既出， 驷马难追 [yī yán jì chū sì mǎ nán zhuī]

1. ■ A promise cannot be taken back once it is made.; A word once out of the mouth cannot be overtaken by swift horses.; A word once spoken cannot be overtaken even by a team of four horses.; A word spoken is past recalling.; One's promise has been given and repentance is now too late.; What is said cannot be unsaid.; When a word has once been spoken, a team of four horses cannot recall it.