The Prose Edda 2.40

"What more is to be said of the gold? Hreidmarr took the gold for his son's wergild, but Fáfnir and Reginn claimed some part of their brother's blood-money for themselves. Hreidmarr would not grant them one penny of the gold. This was the wicked purpose of those brethren: they slew their father for the gold. Then Reginn demanded that Fáfnir share the gold with him, half for half. Fáfnir answered that there was little chance of his sharing it with his brother, seeing that he had slain his father for its sake; and he bade Reginn go hence, else he should fare even as Hreidmarr. Fáfnir had taken the helmet which Hreidmarr had possessed, and set it upon his head (this helmet was called the Helm of Terror, of which all living creatures that see it are afraid), and the sword called Hrotti. Reginn had that sword which was named Refill. So he fled away, and Fáfnir went up to Gnita Heath, and made himself a lair, and turned himself into a serpent, and laid him down upon the gold.

"Then Reginn went to King Hjálprekr at Thjód, and there he became his smith; and he took into his fostering Sigurdr, son of Sigmundr, Völsungr's son, and of Hjördís, daughter of Eylimi. Sigurdr was most illustrious of all Host-Kings in race, in prowess, and in mind. Reginn declared to him where Fáfnir lay on the gold, and incited him to seek the gold. Then Reginn fashioned the sword Gramr, which was so sharp that Sigurdr, bringing it down into running water, cut asunder a flock of wool which drifted down-stream onto the sword's edge. Next Sigurdr clove Reginn's anvil down to the stock with the sword. After that they went, Sigurdr and Reginn, to Gnita Heath, and there Sigurdr dug a pit in Fáfnr's way and laid himself in ambush therein. And when Fáfnir glided toward the water and came above the pit, Sigurdr straightway thrust his sword through him, and that was his end.

"Then Reginn came forward, saying that Sigurdr had slain his brother, and demanded as a condition of reconciliation that he take Fáfnir's heart and roast it with fire; and Reginn laid him down and drank the blood of Fáfnir, and settled himself to sleep. But when Sigurdr was roasting the heart, and thought that it must be quite roasted, he touched it with his finger to see how hard it was; and then the juice ran out from the heart onto his finger, so that he was burned and put his finger to his mouth. As soon as the heart's blood came upon his tongue, straightway he knew the speech of birds, and he understood what the nuthatches were saying which were sitting in the trees. Then one spake:

There sits Sigurdr Blood-besprinkled, Fáfnir's heart With flame he roasteth: Wise seemed to me The Spoiler of Rings If the gleaming Life-fibre he ate.

There lies Reginn—sang another— Rede he ponders, Would betray the youth Who trusteth in him: In his wrath he plots Wrong accusation; The smith of bale Would avenge his brother.

Then Sigurdr went over to Reginn and slew him, and thence to his horse, which was named Grani, and rode till he came to Fáfnir's lair. He took up the gold, trussed it up in his saddle-bags, laid it upon Grani's back, mounted up himself, and then rode his ways. Now the tale is told why gold is called Lair or Abode of Fáfnir, or Metal of Gnita Heath, or Grani's Burden.