At the Back of the North Wind by George MacDonald

DIAMOND woke very early in the morning, and thought what a curious dream he had had. But the memory grew brighter and brighter in his head, until it did not look altogether like a dream, and he began to doubt whether he had not really been abroad in the wind last night. He came to the conclusion that, if he had really been brought home to his mother by Mrs. Crump, she would say something to him about it, and that would settle the matter. Then he got up and dressed himself, but, finding that his father and mother were not yet stirring, he went down the ladder to the stable. There he found that even old Diamond was not awake yet, for he, as well as young Diamond, always got up the moment he woke, and now he was lying as flat as a horse could lie upon his nice trim bed of straw.

"I'll give old Diamond a surprise," thought the boy; and creeping up very softly, before the horse knew, he was astride of his back. Then it was young Diamond's turn to have more of a surprise than he had expected; for as with an earthquake, with a rumbling and a rocking hither and thither, a sprawling of legs and heaving as of many backs, young Diamond found himself hoisted up in the air, with both hands twisted in the horse's mane. The next instant old Diamond lashed out with both his hind legs, and giving one cry of terror young Diamond found himself lying on his neck, with his arms as far round it as they would go. But then the horse stood as still as a stone, except that he lifted his head gently up to let the boy slip down to his back. For when he heard young Diamond's cry he knew that there was nothing to kick about; for young Diamond was a good boy, and old Diamond was a good horse, and the one was all right on the back of the other.