The Lord of the Rings, The Fellowship of the Ring (Book 1), Chapter 1, pg.46 

“Well, that’s that,” he said. “Now I’m off!

They went out into the hall. Bilbo chose his favourite stick from the stand; then he whistled. Three dwarves came out of different rooms where they had been busy.

“Is everything ready?” asked Bilbo. “Everything packed and labelled?”

“Everything,” they answered.

“Well, let’s start then!” He stepped out of the front-door. It was a fine night, and the black sky was dotted with stars. He looked up, sniffing the air. “What fun! What fun to be off again, on the road with dwarves! This is what I have really been longing for, for years! Good-bye!” he said, looking at his old home and bowing to the door. “Good-bye, Gandalf!”

“Good-bye for the present, Bilbo. Take care of yourself! You are old enough, and perhaps wise enough.”

“Take care! I don’t care. Don’t worry about me! I am as happy now as I have ever been, and that is saying a great deal. But the time has come. I am being swept off my feet at last,” he added, and then in a low voice, as if to himself, he sang softly in the dark:

The Road goes ever on and on, down from the door where it began

Now far ahead the Road has gone, and I must follow, if I can

Pursuing it with eager feet, until it joins some larger way

Where many paths and errands meet.

And whither then? I cannot say.

He paused, silent for a moment. Then without another word he turned away from the lights and voices in the fields and tents, and followed by his three companions went round into his garden, and trotted down the long sloping path. He jumped over a low place in the hedge at the bottom, and took to the meadows, passing into the night like a rustle of wind in the grass.

Gandalf remained for a while staring after him into the darkness. “Good-bye, my dear Bilbo - until our next meeting!” he said softly and went back indoors.