There must have circulated a Jewish story about the mad king Nabonidus who went to Temâ to recover his wits, and recognized the supreme God. Two people reworked this original: one of the authors of Daniel changed the name of the monarch, the author of the Prayer changed the illness (to make the story fit Leviticus 13?). The reconstructed story independently confirms two points made by the author of the verse account: Nabonidus suffered from a mental disease and insulted the Babylonian clergy by his monotheistic ideas . This does not prove that Nabonidus was mad, but it makes it extremely plausible that the accusation was very old.
Words of the prayer, said by Nabonidus, king of Babylonia, the great king,
when afflicted with an ulcer on command of the most high God in Temâ:
'I, Nabonidus, was afflicted with an evil ulcer for
seven years, and far from men I was driven, until I
prayed to the most high God. And an exorcist pardoned my sins. He was a Jew from
among the children of the exile of Judah, and said: "Recount this in
writing to glorify and exalt the name of the most high God." Then I wrote
this: "When I was afflicted for seven years by the most high God with an
evil ulcer during my stay at Temâ, I prayed to the gods of silver and
gold, bronze and iron, wood, stone and lime, because I thought and considered
them gods..."' [the end is missing]
(It is interesting to notice that the line 'have praised the gods of silver and gold, bronze and iron, wood and stone' returns in Daniel, just twenty-two lines below the story of the madness of Nebuchadnezzar.)