大義滅親

From Zuo Zhuan. Zhou Yu (州吁) had murdered his brother, Duke Huan of Wey (衛桓公), and taken his place. But he could not gain the favor of the people of Wey. Shi Que (石碏), an officer loyal to the state, devised a scheme and had the usurper killed. Shi Que's son Shi Hou was a close associate of Zhou Yu, so Shi Que had his son killed as well. The people praised his act (《左傳·隱公四年》):

君子曰：「石碏，純臣也，惡州籲而厚與焉。『大義滅親』，其是之謂乎！」 [Classical Chinese, trad.]

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君子曰：「石碏，纯臣也，恶州吁而厚与焉。『大义灭亲』，其是之谓乎！」 [Classical Chinese, simp.]

From: Commentary of Zuo, c. 4^th century BCE, translated based on James Legge's version

Jūnzǐ yuē: “Shí Què, chún chén yě, wù Zhōu Yù ér Hòu yǔ yān. ‘dàyì miè qīn’, qí shì zhī wèi hū!”

A superior man may say, "Shi Que was a minister without blemish. He hated Zhou Yu, with whom his own son Hou was art and part; — and did he not so afford an illustration of the saying that great righteousness is supreme over the affections?"

大義滅親

1. to place righteousness before family​; to be ready to punish one's own family if justice demands it