From The Fellowship of the Ring Tom Bombadil is singing this song when he first meets the hobbits.

Hey dol! merrydol! ring a dong dillo!
Ring a dong! hop along! fal lal the willow!
Tom Bom, jolly Tom, Tom Bombadillo!

Hey! Come merry dol! derry dol! My darling!
Light goes the weather-wind and the feathered starling.
Down along under Hill, shining in the sunlight,
Waiting on the doorstep for the cold starlight,
There my pretty lady is, River-woman’s daughter,
Slender as the willow-wand, clearer than water.
Old Tom Bombadil water-lilies bringing
Comes hopping home again. Can you hear him singing?
Hey! Come merry dol! derry dol! and merry-o,
Goldberry, Goldberry, merry yellow berry-o!
Poor old Willow-man, you tuck your roots away!
Tom’s in a hurry now. Evening will follow day.
Tom’s going home again water-lilies bringing.
Hey! Come merry dol! Can you hear me singing?

Research: legolas19
Editing: Hathaldir