Gregory the Great, on Dan 2:29

“Thou, O king, didst begin to think in thy bed, what should come to pass hereafter: and he that revealeth mysteries shewed thee what shall come to pass.”

“"Thou, O king, diddest begin to think in thy bed, what should happen in times to come; and he that revealeth mysteries did shew thee what things should come:" and a little after: "Thou diddest see, and behold as it were a great statue." Wherefore, seeing Daniel doth with reverence insinuate that the dream should come to pass, and also declareth from what cogitation it did spring, plainly do we learn that dreams sometimes do come both of thought and revelation together. But seeing dreams do grow from such divers roots, with so much the more difficulty ought we to believe them: because it doth not easily appear unto us, from what cause they do proceed. Holy men, indeed, by a certain inward spiritual taste, do discern betwixt illusions and true revelations, by the very voices or representations of the visions themselves: so that they know what they receive from the good spirit, and what they suffer by illusion from the wicked: and therefore, if our mind be not herein very attentive and vigilant, it falleth into many vanities, through the deceit of the wicked spirit: who sometime useth to foretell many true things, that, in the end, he may by some falsehood ensnare our soul. As not long since it is most certain, that it befell to one that lived amongst us, who, being much given to observe dreams, had one night in a dream long life promised him: and when as he had made provision of great store of money for the maintenance of his many days, he was so suddenly taken out of this life, that he left it all behind him, without ever having any use thereof, and carried not with him any good works to the next world.”

Imported from an open dataset — not yet checked against the printed edition.