Without discrimination or judgment. Midas, King of Phrygia, was appointed to judge a musical contest between Apollo and Pan, and gave judgment in favour of the satyr; whereupon Apollo in contempt gave the king a pair of ass's ears. Midas hid them under his Phrygian cap; out his servant, who used to cut his hair, discovered them, and was so tickled at the “joke,” which he durst not mention, that he dug a hole in the earth, and relieved his mind by whispering in it “Midas has ass's ears.” Budaeus gives a different version. He says that Midas kept spies to tell him everything that transpired throughout his kingdom, and the proverb “that kings have long arms” was changed in his case to “Midas has long ears.” “Ex eo in proverbium venit, quod multos otacustas—i.e. auricularios habebat. ” (De Asse.) (See Pope: Prologues to Satires.)
Domenichino (1581-1661) has a painting on the Judgment of Midas.
Midas has ass's ears. An exact parallel of this tale is told of Portzmach, king of a part of Brittany. It is said Portzmach had all the barbers of his kingdom put to death, lest they should announce to the public that he had the ears of a horse. An intimate friend was found willing to shave him, after swearing profound secrecy; but not able to contain himself, he confined his secret to the sands of a river bank. The reeds of this river were used for pan-pipes and hautbois, which repeated the words “Portzmach- King Portzmach has horse's ears.”
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894