告到陰司 The Dragon Complains Below
因他夢斬了涇河龍王，那龍王告到陰司，說我王許救又殺之，故我王遂得促病，漸覺身危。魏徵又寫書一封，與我王帶至陰司，寄與酆都城判官崔珏。因他梦斩了泾河龙王，那龙王告到阴司，说我王许救又杀之，故我王遂得促病，渐觉身危。魏征又写书一封，与我王带至阴司，寄与酆都城判官崔珏。
逐句解 Line by line
"Because he beheaded the Dragon King of the Jing River in a dream, that dragon laid a complaint in the world below, saying my sovereign had promised to save him and then killed him; and so my sovereign fell suddenly ill and felt his life come into danger."
得 is dé, to contract — in Chinese as in English one gets an illness the way one gets anything else. 促病 is a sickness that comes on fast; the first character carries the sense of being pressed or hurried.
"Wei Zheng then wrote a letter and gave it to my sovereign to carry down to the world below, addressed to Cui Jue, the judge of the city of Fengdu."
都 is dū in 酆都, the city of the dead — the same reading as the 都會 of the capital rhapsody, and not the dōu of 'all'.
The dragon's complaint is a lawsuit. He does not accuse the minister who killed him; he accuses the king who promised to prevent it, and the charge is breach of an undertaking rather than murder. That is what makes the case heard at all.
And the remedy Wei Zheng offers is more paperwork. Having caused the problem by carrying out a sentence in his sleep, he writes a letter of introduction to the clerk who keeps the register. The whole affair is conducted between officials, in writing, across the boundary of death.