一言既出，驷马难追(Yī yán jì chū，sì mǎ nán zhuī)Once uttered, words cannot be taken back, even by riding a four-horse chariot.

Explanation

"一言既出，驷马难追”这句话字面义是指话一旦说出口，就连套着四匹马的车也追不回来。形容话一旦说出口，就不能再收回，一定要做到。
“一言既出，驷马难追” literally means that once something is said, the words uttered cannot be taken back even by riding them down on a four-horse chariot. It means that what is said cannot be taken back, so one should keep promises.

Words:

演出yǎnchū:show;
承诺chénɡnuò:promise.

Sentences

1. Jiǎ：Jìdé míngtiān yídìng yào qù kàn wǒ de yǎnchū !
甲：记得明天一定要去看我的演出！
A: Please remember to see my show tomorrow.

Yǐ：Yī yán jì chū，sì mǎ nán zhuī。Míngtiān yídìng qù!
乙：一言既出，驷马难追。明天一定去！
B: Words once uttered cannot be taken back even by riding a four-horse chariot. I’ll definitely be there tomorrow!

2.Jiǎ: Duìbuqǐ，kǒngpà shǔjià wǒ bùnéng gēn nǐ yìqǐ qù lǚyóu le。
甲：对不起，恐怕暑假我不能跟你一起去旅游了。
A: Sorry, I’m afraid I can’t travel together with you this summer vacation.

Yǐ：Súhuà shuō：Yī yán jì chū，sì mǎ nán zhuī。 Nǐ zěnme néng bù shǒu chéng nuò ne?
乙：俗话说：一言既出，驷马难追。你怎么能不守承诺呢？
B: As the saying goes, “Words once uttered cannot be taken back even by riding on a four-horse chariot.” How dare you go back on your word?

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