金口玉言 Golden words
Explanation
原指皇帝的言论不可更改。现多用来形容说话非常有权威，不可更改。
Originally referred to the emperor's pronouncements being unchangeable. Now mostly used to describe someone's words being very authoritative and unchangeable.
Origin Story
话说唐朝时期，有一位名叫李白的诗仙，他不仅诗词歌赋写得极好，而且非常善于言谈。有一次，李白参加宫廷宴会，皇帝唐玄宗亲自作陪。席间，唐玄宗问李白：“爱卿，你认为我的诗词写得如何？”李白不慌不忙地回答道：“陛下，您的诗词气势磅礴，如同黄河之水奔腾不息，令人叹为观止！”唐玄宗听后龙颜大悦，连连点头称赞。席间，唐玄宗又问李白对自己的书法有何评价。李白想了想，说：“陛下，您的书法刚劲有力，如行云流水般飘逸自然，堪称绝世佳作！”唐玄宗听完以后，更加高兴，觉得李白评价得十分到位，便赏赐了许多金银财宝。后来，人们便将唐玄宗的言论称为“金口玉言”，意思是他的话语如同金玉一般珍贵，不可更改。从此以后，“金口玉言”便成为了一个家喻户晓的成语，用来形容那些说话有权威性，不容置疑的人。
It is said that during the Tang Dynasty, there was a poet named Li Bai, who not only wrote excellent poems and songs, but also was very eloquent. Once, Li Bai attended a court banquet, with Emperor Xuanzong of Tang personally accompanying him. During the banquet, Emperor Xuanzong asked Li Bai, "My dear, what do you think of my poems?" Li Bai calmly replied, "Your Majesty, your poems are magnificent and powerful, like the Yellow River water rushing endlessly, which is breathtaking!" Emperor Xuanzong was overjoyed and nodded approvingly. During the banquet, Emperor Xuanzong again asked Li Bai for his evaluation of his calligraphy. Li Bai thought for a moment and said, "Your Majesty, your calligraphy is powerful and energetic, like flowing clouds and water, elegant and natural, it is a masterpiece!" After hearing this, Emperor Xuanzong was even happier, feeling that Li Bai's evaluation was very accurate, so he rewarded him with many gold and silver treasures. Later, people called Emperor Xuanzong's words "golden words," meaning that his words are as precious as gold and jade, and cannot be changed. From then on, "golden words" became a household idiom, used to describe those whose words are authoritative and undeniable.
Usage
用于形容说话非常有权威，不容置疑。
Used to describe someone's words as being very authoritative and undeniable.
Examples
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皇帝金口玉言，一言九鼎。
huangdi jinkouyu yan, yiyanyujiuding
The emperor's word is law.
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他金口玉言，答应的事情一定会做到。
ta jinkouyu yan, daying deshiqing yiding hui zuodao
His word is his bond. He always keeps his promises.