The Prose Edda 1.44

Then spake Gangleri: "'A good ship is Skídbladnir, but very great magic must have been used upon it before it got to be so fashioned. Has Thor never experienced such a thing, that he has found in his path somewhat so mighty or so powerful that it has overmatched him through strength of magic?" Then said Hárr: "Few men, I ween, are able to tell of this; yet many a thing has seemed to him hard to overcome. Though there may have been something so powerful or strong that Thor might not have succeeded in winning the victory, yet it is not necessary to speak of it; because there are many examples to prove, and because all are bound to believe, that Thor is mightiest." Then said Gangleri: "It seems to me that I must have asked you touching this matter what no one is able to tell of. Then spake Jafnhárr: "We have heard say concerning some matters which seem to us incredible, but here sits one near at hand who will know how to tell true tidings of this. Therefore thou must believe that he will not lie for the first time now, who never lied before." Gangleri said: "Here will I stand and listen, if any answer is forthcoming to this word; but otherwise I pronounce you overcome, if ye cannot tell that which I ask you."

Then spake Thridi: "Now it is evident that he is resolved to know this matter, though it seem not to us a pleasant thing to tell. This is the beginning of this tale: Öku-Thor drove forth with his he-goats and chariot, and with him that Ás called Loki; they came at evening to a husbandman's, and there received a night's lodging. About evening, Thor took his he-goats and slaughtered them both; after that they were flayed and borne to the caldron. When the cooking was done, then Thor and his companion sat down to supper. Thor invited to meat with him the husbandman and his wife, and their children: the husbandman's son was called Thjálfi, and the daughter Röskva. Then Thor laid the goat-hides farther away from the fire, and said that the husbandman and his servants should cast the bones on the goat-hides. Thjálfi, the husbandman's son, was holding a thigh-bone of the goat, and split it with his knife and broke it for the marrow.

"Thor tarried there overnight; and in the interval before day he rose up and clothed himself, took the hammer Mjöllnir, swung it up, and hallowed the goat-hides; straightway the he-goats rose up, and then one of them was lame in a hind leg. Thor discovered this, and declared that the husbandman or his household could not have dealt wisely with the bones of the goat: he knew that the thighbone was broken. There is no need to make a long story of it; all may know how frightened the husbandman must have been when he saw how Thor let his brows sink down before his eyes; but when he looked at the eyes, then it seemed to him that he must fall down before their glances alone. Thor clenched his hands on the hammer-shaft so that the knuckles whitened; and the husbandman and all his household did what was to be expected: they cried out lustily, prayed for peace, offered in recompense all that they had. But when he saw their terror, then the fury departed from him, and he became appeased, and took of them in atonement their children, Thjálfi and Röskva, who then became his bond-servants; and they follow him ever since.