空口无凭 Empty words
Explanation
指没有证据，单凭空话，不足为凭。
Means that claims without evidence or proof are not credible.
Origin Story
从前，有个秀才，他自诩才华横溢，却屡试不第。一日，他向邻里夸耀，说自己这次一定能考中状元，并绘声绘色地描述了金榜题名、衣锦还乡的盛况。邻里半信半疑，纷纷表示要等他考中后才能相信。秀才见众人不信，无奈地叹了口气，说：“空口无凭啊！”后来，秀才再次落榜，邻里们都嘲笑他夸夸其谈，空口无凭。
Once upon a time, there was a scholar who considered himself exceptionally talented, yet he repeatedly failed the imperial examinations. One day, he boasted to his neighbors that he would definitely pass the exam and become the top scholar this time, vividly describing the glory of success and his triumphant return. His neighbors were dubious, saying they would only believe him once he actually succeeded. Seeing their disbelief, the scholar sighed helplessly, "Empty words are no proof!" Later, when he failed again, his neighbors mocked him for his empty boasts.
Usage
多用于否定句，指说话没有证据，不可靠。
Often used in negative sentences, meaning that a statement without proof is unreliable.
Examples
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空口无凭，你得拿出证据来！
kōng kǒu wú píng, nǐ děi ná chū zhèngjù lái!
Empty words are no proof, you must produce evidence!
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光说不练假把式，空口无凭，我们不会相信你的话的。
guāng shuō bù liàn jiǎ bǎshì, kōng kǒu wú píng, wǒmen bù huì xiāngxìn nǐ de huà de
Actions speak louder than words, empty words are not proof, we won't believe your words.