The Hobbit, Chapter 7

Beorn left and changed shapes (into a bear), after which he sought to determine in the tale he'd been told was true.

So they all went to breakfast with him. Beorn was most jolly for a change; indeed he seemed to be in a splendidly good humour and set them all laughing with his funny stories; nor did they have to wonder long where he had been or why he was so nice to them, for he told them himself. He had been over the river and right back up into the mountains-from which you can guess that he could travel quickly, in bear's shape at any rate. From the burnt wolf-glade he had soon found out that part of their story was true; but he had found more than that: he had caught a Warg and a goblin wandering in the woods. From these he had got news: the goblin patrols were still hunting with Wargs for the dwarves, and they were fiercely angry because of the death of the Great Goblin, and also because of the burning of the chief wolf's nose and the death from the wizard's fire of many of his chief servants. So much they told him when he forced them, but he guessed there was more wickedness than this afoot, and that a great raid of the whole goblin army with their wolf-allies into the lands shadowed by the mountains might soon be made to find the dwarves, or to take vengeance on the men and creatures that lived there, and who they thought must be sheltering them.