fēi yī rì zhī gōng
Meaning: Cannot be done in one day, e.g. Rome was not built in one day (罗马非一日之功)
Xi Jinping used this suyu in a
at a forum about the protection and development of the Yellow River on September 18th, 2019.
Here's another similar, commonly used expression:
dòng sǎn chǐ fěi yǐ rì zhī
Meaning: ice three feet thick can't be frozen in one day.