一言既出，驷马难追。
(Yìyán jì chū, sìmǎ nán zhuī)
A team of horses will struggle to chase down a spoken word.
- "The Analects of Yan Yuan" (《论语·颜渊》), -
it means a word spoken can never be taken back or a promise must be kept.
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Happy holiday!
BalasPadam