Records of the Three Kingdoms
Fei Yi, courtesy name Wenwei, was from Meng in Jiangxia. He came into Shu as a student. After Liu Bei named an heir, Fei Yi and Dong Yun were gentlemen of the household. When Zhuge Liang returned from the southern campaign, officials went out tens of li to meet him. Zhuge Liang sent the official boat first to fetch Fei Yi and Dong Yun. The gesture shows the regard. Fei Yi went to Wu more than once. Sun Quan tested him with wine and jokes. He neither got drunk nor lost the thread. Sun Quan called him a man of quiet virtue in Shu.
After Jiang Wan’s death Fei Yi, as senior general, ran the secretariat. Jiang Wei wanted large northern campaigns. Fei Yi usually kept the troops given to him under ten thousand, on the ground that the state could not bear more. At the new-year assembly of 253 the Wei defector Guo Xun was present. Fei Yi drank until he was drunk, and Guo Xun stabbed him. Chen Shou says he was generous and carried on what Zhuge Liang had set in place.
Romance of the Three Kingdoms
In the novel Fei Yi is the steady regent after Zhuge Liang. He tells Jiang Wei more than once not to campaign every year. The missions to Wu, and the fact that he does not disgrace them, are there too.
The assassination is at a feast. The book makes Guo Xun an assassin who has waited, and Fei Yi is still laughing when he dies. After that chapter nobody in Chengdu limits Jiang Wei’s numbers.
Reference: Wikipedia · Fei Yi