Xu Shu serves Cao Cao

In Romance of the Three Kingdoms novel, Cao Cao was impressed by Xu Shu's intelligence and brilliance after helping Liu Bei defeat Cao Ren and so he wanted Xu Shu to serve him. The story goes that Cao Cao invited Xu Shu's mother to write a letter to her son to come to Xuchang, but she refused and told Cao Cao was a traitor and that him serving Liu Bei is an honor. This made Cao Cao furious. He ordered her to be executed, but Cheng Yu insisted him not to do it, otherwise this would make Xu Shu angry and seek revenge against him.