請君入甕

From the story of Lai Junchen's questioning of Zhou Xing, who were both secret police officials and famous for torturing dissidents:

唐秋官侍郎周興與來俊臣對推事。俊臣別奉進止鞫興，興不之知也。及同食，謂興曰：「囚多不肯承，若為作法？」興曰：「甚易也。取大甕，以炭四面炙之，令囚人處之其中，何事不吐！」即索大甕，以火圍之，起謂興曰：「有內狀勘老兄，請兄入此甕。」興惶恐叩頭，咸即款伏。 [Classical Chinese, trad.]

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唐秋官侍郎周兴与来俊臣对推事。俊臣别奉进止鞫兴，兴不之知也。及同食，谓兴曰：「囚多不肯承，若为作法？」兴曰：「甚易也。取大瓮，以炭四面炙之，令囚人处之其中，何事不吐！」即索大瓮，以火围之，起谓兴曰：「有内状勘老兄，请兄入此瓮。」兴惶恐叩头，咸即款伏。 [Classical Chinese, simp.]

From: 7^th century CE, Zhang Zhuo, Chaoye Qianzai (《朝野僉載》)

Táng qiūguān shìláng zhōuxìng yǔ láijùnchén duì tuīshì. Jùnchén bié fèngjìnzhǐ jū xìng, xìng bù zhī zhī yě. Jí tóng shí, wèi xìng yuē: “Qiú duō bùkěn chéng, ruò wèi zuòfǎ?” Xìng yuē: “Shèn yì yě. Qǔ dà wèng, yǐ tàn sìmiàn zhì zhī, lìng qiúrén chù zhī qí zhōng, héshì bù tù!” Jí suǒ dà wèng, yǐ huǒ wéi zhī, qǐ wèi xìng yuē: “Yǒu nèizhuàng kān lǎoxiōng, qǐng xiōng rù cǐ wèng.” Xìng huángkǒng kòutóu, xián jí kuǎnfú.

In the Tang Dynasty, Zhou Xing and Lai Junchen were judges of the Ministry of Justice. One day, Lai Junchen received an edict to interrogate Zhou Xing , and Zhou did not know about that. When they were having lunch, Lai asked Zhou, "Most of the criminals are not willing to admit . How would you deal with them then?" Zhou then answered, "That's easy. Get a big jar, heat it with charcoal, then ask the criminal to get into it. He'll definitely admit everything." Lai then take a big jar and then set up fire around the jar. He stood up and then told Zhou, "I received an order to question you. Now, please get into this jar." Zhou then panicked and kowtowed, and then pleaded guilty immediately.

請君入甕

1. to pay back in someone's own coin; to give someone a taste of his/her own medicine; to make someone's act backfire on him or her; to treat someone in his or her own ways

• 以其人之道，還治其人之身／以其人之道，还治其人之身 (yǐ qí rén zhī dào, huán zhì qí rén zhī shēn)