Barrow-wights: History (p2)

There they were almost slain by a wight; three of the Hobbits had been lain in a barrow filled with a strange green light and were dressed in white robes and wore jewels and gold and had a sword across their necks. The wight had finished an incantation, and was preparing to finish them off when Frodo summoned up the courage to slice off its hand; he then called upon Tom Bombadil when the wight extinguished the dim light in the cavern. Bombadil performed some kind of exorcism on the barrow, through the rare power of his singing, which caused the wight to flee with a shriek; he then gave the hobbits swords and spread out the gold and treasures from the barrow on the grass, so that the barrow's spell was broken and no wight could make habitat there.