一言既出,驷马难追
Yī yán jì chū, sì mǎ nán zhuī


Translation:
Once one’s word has been given, even a team of four horses cannot take it back.
Meaning:
What one has said cannot be unsaid; one must be careful about making promises and faithful in honoring those promises.

Vocabulary

Character Pinyin English
one (Nu)
yán word (N)
already (Adv, Conj)
chū to go out (V); here: to be said (V)
驷马 sì mǎ a team of four horses (N)
nán difficult, hard (Adj)
zhuī to take back (V)

Examples
一言既出,驷马难追。作为企业领导,一定要努力实现对员工的任何承诺。
A promise is a promise. As the leader of the enterprise, you must try to honor the promises you have made to your employees.