一言既出，驷马难追（一言既出，駟馬難追）　

◎ 一言既出，驷马难追 yī yán jì chū,sìmǎ nán zhuī

[what has been said cannot be unsaid;A word spoken is past recalling; A word published cannot be recalled] 话已说出口,就是四匹马拉的车也无法追回。形容说话要算数,说出就不能收回