闭口不言 remain silent
Explanation
指紧闭嘴唇，一句话也不说。形容沉默不语，或因某种原因而保持沉默。
It means to close one's lips tightly and not say a word. It describes silence or silence for some reason.
Origin Story
话说唐朝时期，有一个名叫李白的诗人，他一生豪放不羁，爱酒如命，也爱说大话。有一次，他喝醉了酒，在长安街头信口开河，夸下海口说自己能喝掉黄河水。这话传到了唐玄宗的耳朵里，玄宗皇帝很好奇，便召见了他。在皇宫里，李白依然大言不惭，又说了一些狂妄之言。玄宗皇帝虽然欣赏他的才华，但也对他的行为感到不满，于是便训斥了他一番。李白虽然酒醒了一些，但也知道自己说错了话，便闭口不言，再也不提此事。从此以后，李白变得谨慎了许多，不再像以前那样口无遮拦了。
In the Tang Dynasty, there was a poet named Li Bai, who was known for his unrestrained personality, love of alcohol, and tendency to boast. Once, while drunk, he bragged in the streets of Chang'an that he could drink up the Yellow River. This reached the ears of Emperor Xuanzong, who summoned him. In the imperial palace, Li Bai continued his boasting, prompting the Emperor to reprimand him. Li Bai, slightly sobered, realized his mistake and remained silent, never mentioning it again. From then on, Li Bai became more cautious, avoiding reckless words.
Usage
常用来形容人因为某种原因而保持沉默，或不愿开口说话。
Often used to describe someone who remains silent due to some reason, or unwilling to speak.
Examples
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庭审上，被告人闭口不言，拒不认罪。
tíngshěnshang, bèigàorén bìkǒubùyán, jùbùrènzuì
In court, the defendant remained silent and refused to plead guilty.
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面对记者的提问，他闭口不言，一言不发。
miànduì jìzhě de tíwèn, tā bìkǒubùyán, yīyánbùfā
Faced with reporters' questions, he remained silent.
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遭受了不白之冤，他选择了闭口不言，任凭别人诽谤。
zāoshòule bùbái zhīyuān, tā xuǎnzéle bìkǒubùyán, rèn'píng biérén fěibàng
Suffering from injustice, he chose to remain silent and let others slander him.