Zhang Xiu, nephew of the late Dong Zhuo general Zhang Ji, took command of his uncle's army after Zhang Ji's death. Soon after, Cao Cao attacked Nanyang, and Zhang Xiu surrendered. But not long after, Zhang Xiu betrayed Cao Cao, dealing him a devastating defeat: Cao Cao's beloved horse "Shadowless" was shot, his own right arm was wounded, and his eldest son Cao Ang gave up his own horse to save his father, losing his life. Zhang Xiu then fled to Liu Biao, clashing with Cao Cao in several more battles. Yet three years later, when Zhang Xiu surrendered again, Cao Cao not only spared him but granted him a noble title, saying, "A man who forgives past grievances and welcomes talent is one who builds an empire." This act of magnanimity turned a former enemy into a loyal ally.
During the Three Kingdoms period, the warlord Cao Cao had once recommended Wei Zhong as a "Filial and Incorrupt" candidate, placing Wei in his debt. When Yanzhou rebelled, Cao Cao believed that even if everyone else betrayed him, Wei Zhong would not. Later, hearing that Wei Zhong had fled to save his life, Cao Cao angrily swore, "Wei Zhong, unless you flee to the far south or the northern barbarians, I will never let you off!" Yet when Cao Cao captured Shequan City and took Wei Zhong alive, he valued Wei's talent so much that he personally untied his bonds and appointed him Governor of Henei, placing him in charge of the lands north of the Yellow River.
There were also Zang Ba, Sun Guan, and Wu Jing, who had previously followed Lü Bu in opposing Cao Cao. After Lü Bu was defeated and killed, Zang Ba and the others were captured, but Cao Cao treated them well, granting them the coastal lands of Xu Province and Qing Province to govern.
Cao Cao, for the sake of his great enterprise, set aside personal grudges and sought talent widely. Thus, the author of *Records of the Three Kingdoms* praised him as "bearing no grudge for past wrongs." Later, the idiom "bearing no grudge for past wrongs" came to describe not holding onto old grievances.
Source: *Records of the Three Kingdoms*, Chapter "Biography of Emperor Wu"
Meaning of the Idiom: Later, the Chinese idiom "不念旧恶" came to describe not holding onto old grievances.