Where does "the son of heaven protects the country and the king dies" come from?

These two sentences are from the Ming Dynasty, one from the early Ming Dynasty and the other from the late Ming Dynasty.

Emperor Defends the Country: At the beginning of the Ming Dynasty, Zhu Yuanzhang made Nanjing his capital, but the rule of Meng Yuan remained in the memory of the Han nationality. In order to resist and destroy the Northern Yuan Dynasty, Zhu Yuanzhang enfeoffed several sons in the northern frontier. Later, the prince of Yan, who was enfeoffed in Beijing, was unable to succeed to the throne and obtained the throne, which was called Cheng Zu in history. He later moved to Beijing. Although Beijing is his old base area, it is close to Shanhaiguan, Jimen and Datong, one of the nine sides. Later, based in Beijing, Ming Chengzu attacked on a large scale and made five expeditions, defeating the forces of the Northern Yuan Dynasty.

The king died in his country: the Ming emperor had a great advantage, that is, good moral integrity. Even in the Nanbeibao Rebellion, Ming Yingzong, who was captured, didn't have the backbone to surrender (compare the two emperors of the Song Dynasty, Qin Hui). When the Ming Dynasty perished, the last emperor Chongzhen refused to move the capital to the south of the Yangtze River, hanged himself after sending the prince away, and urged his empresses to commit suicide and beheaded the princess himself, so he was called "the king".