During the Song Dynasty, the upright official Chen Cisheng served three times as an imperial censor, never echoing others' opinions but daring to speak the truth, repeatedly submitting memorials to the emperor impeaching corrupt ministers.
During the reign of Emperor Zhezong of the Song Dynasty, the powerful ministers Zhang Dun and Cai Bian formed a clique to advance their own interests. Chen Cisheng had been demoted early in Zhezong's reign, and Zhang and Cai assumed he bore a grudge. Since Cai Bian was also from the same hometown as Chen, they tried to recruit him to help oust other officials, but Chen sternly refused. This made Zhang and Cai hate him deeply, so they slandered him to the emperor, urging his exile from the capital. Fortunately, Emperor Zhezong was wise and said, "Flattering ministers are easy to find, but Chen Cisheng speaks the truth—such a man is rare and should not be punished." Instead, he promoted Chen to Left Remonstrance Official, tasked with offering honest counsel.
During the Song Dynasty, the censor Chen Cisheng repeatedly impeached the powerful minister Zhang Dun and his faction before Emperor Zhezong, but his warnings went unheeded. When Emperor Huizong ascended the throne, Chen was promoted to imperial advisor and again submitted fierce memorials exposing the crimes of Zhang Dun, Zeng Bu, Cai Bian, and Cai Jing. In his famous "Third Impeachment of Cai Jing," Chen wrote: "Cai Jing nitpicks others' faults and slanders scholar-officials with malicious intent; his poisonous influence has spread across the empire, making it unbearable to hear and unbearable to see. Though Zhang Dun was the mastermind, most of the evil deeds were carried out by Cai Bian. People regard Cai Jing as a man with a smiling face but a venomous heart—this is known to all under heaven."
In the end, these treacherous ministers were all demoted and banished from the capital.
The idiom "Smiling Yaksha" refers to someone who wears a smile but has a venomous heart. In Buddhist scriptures, a yaksha is a man-eating demon, often used to describe someone ugly and vicious.
Source: Chen Cisheng (Song Dynasty), *Memorial Impeaching Cai Jing, Third Memorial*
Meaning of the Idiom: Later, the Chinese idiom "笑面夜叉" came to describe how someone wears a smile but has a venomous heart.