三sān令lìng五wǔ申shēn

Literal: order three times, reiterate five
Figurative: To issue an order or warning again and again, usually from some authority; often said when people still ignore it.

Where does 三令五申 come from?

It is told in the 《史记》, in the biography of Sun Wu, author of The Art of War. King Helü of Wu wanted to test him and let him drill the palace ladies. Sun Wu split them into two companies, put the king's two favorite concubines in command and explained the orders again and again. When the drum sounded, the ladies laughed; he blamed himself for not being clear and repeated the instructions, and they laughed again. Since the orders were now clear, he had the two leaders executed despite the king's pleas, and from then on they all obeyed. Today it is said of repeated warnings.

Source (出处): 《史记·孙子吴起列传》

How is 三令五申 used? Two examples

学xué校xiào三sān令lìng五wǔ申shēn不bù许xǔ带dài手shǒu机jī进jìn教jiào室shì，可kě还hái是shì有yǒu学xué生sheng偷tōu偷tōu带dài。
The school has warned again and again that phones aren't allowed in class, but some students still sneak them in.
我wǒ妈mā三sān令lìng五wǔ申shēn让ràng我wǒ晚wǎn上shang十shí点diǎn前qián回huí家jiā，我wǒ还hái是shì经jīng常cháng迟chí到dào。
My mom has told me over and over to be home by ten, and I'm still often late.

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