Uphold justice at the cost of one's blood relation--Da Yi Mie Qin

The Chinese of this idiom "Uphold justice at the cost of one's blood relation--Da Yi Mie Qin" is 大义灭亲.

During the Spring and Autumn Period (770-476BC), there was many dukedoms under the king of the Eastern Zhou Dynasty.
These dukedoms often fought one another to expand their territories. And within a dukedom, the struggle for power frequently occurred. A typical case was the murder of the Duke of Wei by his younger brother Zhou Xu.

Zhou Xu committed the crime with the help of an important official called Shi Hou. Eventually, Zhou Xu became duke himself. Then he launched wars against other dukedoms and the people suffered. There were complaints and resentments all around.

When he learned about this, Zhou Xu was worried. He talked with Shi Hou about how to stabilize the situation and win back people's confidence. Shi Hou said:"That's easy. I'll ask my father to speak for us. He is highly esteemed by all the officials and the people. I'm sure he'll help us out."

Shi Hou's father, Shi Que, had been a high-ranking official serving under the former duke. He resigned when Zhu Xu seized power. He hated Zhou Xu for his murder of the former duke. He also hated his own son, Shi Hou, for his part in the murder.
Now, Shi Hou came and asked him for help. the father said, "A duke' ascendance to power should be granted by the king. If the king approved it, all the problems will be solved."

"But how can we bet the king's approval?" Shi Hou asked his father. The old man said, "The Duke of Chen is trusted by the king and his dukedom has good relationship with ours. If you and Zhou Xu go to the Duke of Chen and ask him for help, I'm sure he is willing to say a good word for you before the king."

Shi Hou passed his father's word to Zhu Xu and they went to the Dukedom of Chen. But before they arrived, the old man sent an express letter in secret to the Duke of Chen asking him to kill the two murderers.

As soon as Zhou Xu and Shi Hou arrived in the Dukedom of Chen, they were arrested. Some officials from Wei made a special trip to Chen to kill the two men. They put Zhou Xu to death but hesitated to kill Shi Hou because of his father. When the old man learnt about this, he said firmly :'My son has also committed the murder of the duke. What's the good to have him in the world!" he sent his own man to Chen and beheaded Shi Hou.

Later historians commented: "To safeguard the interest of the country, Shi Que did not bend the law for the benefit of his relative. It's really a case of cutting off consanguinity for the sake of righteousness!" Hence comes the idiom "Uphold justice at the cost of one's blood relation".

大义灭亲
春秋时期，在东周周天子的统治下有许多小公国。这些国家常常为了扩大自己的领土而互相争斗。而且，在一个公国内部，权力之争也时常发生。卫国的州吁杀害自己的哥哥――卫国的公爵就是一个典型的例子。
在一个重要的大臣石厚的帮助下，州吁杀害了他的哥哥。最后，他作了卫国的公爵。接着，他发动了同其他公国的战争，使卫国人民经受了很多痛苦。人们怨声载道。
州吁对此也很担忧。他与石厚商量如何巩固政局，赢得百姓的信任。石厚说："这个容易。大臣和百姓们都十分尊敬我的父亲，我去请他出来为我们说话。这样我肯定他能帮我们解决这个问题。"
石厚的父亲石碏曾是前任公爵的上卿。州吁夺权后，他辞去了官职。他痛恨州吁杀害了前任公爵。 同时，他也恨自己的儿子石厚，因为他参与了这场谋杀。 现在，石厚来向他求助。石碏说："诸侯接位，应该得到周天子的许可。只要他同意了，所有的问题都好解决。
"可是怎么让周天子会同意吗？" 石厚问。老人说："陈国公爵受到周天子的信任，而且陈国和我国关系很好。如果你和州吁先去陈国,向他求助，我肯定他会乐意在周天子面前为你们说好话的。"
石厚把他父亲的主意告诉了州吁，然后他们来到了陈国。但在他们到达前，石碏已经秘密快信送至陈国公爵，要求他杀死这两名凶手。
州吁和石厚一到陈国，就被抓了起来。卫国的大臣特地到陈国去执法处死这两个人。他们斩了州吁，但对石厚是否要被斩首很迟疑，因为他毕竟是石碏的亲儿子。 当老人得知这个情况后，他坚定的说："我儿子杀卫公有罪，留他在这世上何用？" 他派家臣去陈国斩了石厚。
后来，史学家们评论道："为了维护国家的利益，石碏不因亲人而违法。实在是大义灭亲呀！"成语"大义灭亲"由此而来。