The story was one of Ennis' staple performance pieces during the sixties and seventies. It occurs, in English, on the Leader lp and often enough on private tapes. Unfortunately while most stories from the lp are transcribed in he Ennis book, this one didn't make it in. I have heard him tell it a few times in real life.
It's easily retrieved on the web:
...Seamus Ennis’s story of a piper who had the courage to spend a night hiding near a fairy rath to listen to the wonderful music of the little folk. As usual they returned to the rath at sunrise to sleep, the nights’ festivity over, and the piper crept out from hiding. On close investigation of the site he found a tiny gold ring on the ground, dropped by a fairy reveller. The very next evening he returned to the rath and hid in the same place to listen again to the music of the wee folk but this time he also overheard the lamenting of a fairy piper over the loss of the ring. The fairy cried that he would grant any wish to get it back, upon which he man stepped from hiding and offered to return the ring, explaining how he found it lost. True to his word the fairy granted the human one wish, and asked the piper to name it. ‘The jig I heard the other night,’ said the man, who added he could not quite remember it (due to the fairies blocking the memory of their tunes), and the fairy piper granted the wish on the spot—the tune that has ever since been called in memory of the incident “The Gold Ring.”
' "The Gold Ring" - there's a story attached to the name. A long, long time ago - if I were there then, I wouldn't be there now; if I were there then and now, I would have a new story or an old story, or I might have no story at all - the birds could talk, giants roamed the land, and fairy music filled the air. There was a farmer, and he was walking across the fields one night, when he heard the faint strains of music in the distance. Moving closer, he saw a fairy piper playing a fairy dance. But when the fairies sensed his presence, they scattered into the woods and vanished into the earth. The farmer went up to the place where the piper had played and there he found a tiny gold ring lying on the ground. So he put it in his pocket, carried it home, and took out his fiddle to celebrate his good fortune with a few reels. But when he put the bow across the strings, he couldn't get a decent sound of it at all, save for the scratching of an old key in an old lock. And no matter how much he played that fiddle, not a note could he get out of it.
So the next night, he returned with the ring and his fiddle to the place where he had found the fairies, and he waited and he waited. And just as the first glimmer of dawn appeared over the eastern sky, he heard the faint rustle of soft feet on golden leaves. When he turned around, he came face to face with the fairy piper.
"I've come for what is mine," says the piper. "For if truth be told, I can't play a slide or a jig or a reel without that ring." "You can have it and welcome," said the farmer. "For if truth be told, I can't play a slide or a jig or a reel with it." And he tossed the ring back, and took out his fiddle, and played the finest reel of his life. And the fairy piper picks up the ring, and takes out his pipes, and plays the finest jig that human ears had ever heard. "Would you ever be after teaching me that tune?" asked the farmer. "I would so," says the fairy piper, and they sat down together until the farmer had it. "And what would it be called?" asked the farmer. "The Gold Ring," says the fairy piper, disappearing into the half-light of dawn.'
There's another, unrelated, tune called the Gold Ring of which it is sometimes suggested the title refers to 'The Fáinne'
, the ring shaped badge that was worn to show the wearer's preparedness to speak Irish