Records of the Three Kingdoms
Dong Cheng was a nephew of Empress Dowager Dong, mother of Emperor Ling. Under Emperor Xian he was general of chariots and cavalry. His daughter was an Honored Consort. Liu Bei’s biography says that in 199 the emperor’s uncle Dong Cheng received a secret edict hidden in a girdle, ordering Cao Cao’s death. Liu Bei joined the plan. In 200 it leaked and Dong Cheng and the others were killed. Liu Bei had already left the capital on the pretext of attacking Yuan Shu, so he did not die in the case.
The girdle edict is in Chen Shou’s text. It is not an object invented by the novel. The full wording and the list of conspirators differ in length from source to source.
Romance of the Three Kingdoms
The novel has the emperor bite his finger and write the edict in blood on a girdle, which Dong Cheng carries out of the palace. Liu Bei signs at Dong Cheng’s house and then hides his intent by gardening. After the conversation on heroes over warm wine, he finds a reason to leave the capital.
When the plot breaks, Dong Cheng is executed and the pregnant Consort Dong is killed. Those scenes turn a failed conspiracy into a moral play between Emperor Xian and Cao Cao. The blood writing is the novel’s way of telling it.
Reference: Wikipedia · Dong Cheng