The Prose Edda on Brynhild
The Younger Edda: > Chapter Iv. > The Niflungs And Gjukungs.
attestation: Brynhild sat on Hindfell surrounded by the Vafurloge flame, having vowed to marry only the man who dared ride through it
"She sat on Hindfell, and her hall was surrounded by the bickering flame called the Vafurloge, and she had made a solemn promise not to wed any other man than him who dared to ride through the bickering flame."
attestation: Brynhild and Gudrun quarreled while washing hair in the river; Brynhild claimed she had a more high-minded husband
"Brynhild waded from the river bank into the stream, and said that she could not bear to have that water in her hair that ran from Gudrun's hair, for she had a more high-minded husband."
attestation: Brynhild incited Gunnar and Hogne to kill Sigurd; being sworn brothers they had their stepbrother Guthorm do it
"Thereupon she egged Gunnar and Hogne to kill Sigurd; but being sworn brothers of Sigurd, they egged Guthorm, their brother, to slay Sigurd."
attestation: Brynhild killed herself with a sword and was cremated on the same pyre as Sigurd
"Then Brynhild pierced herself with the sword and was cremated with Sigurd."