Guðrúnarhvöt is one of the heroic poems of the Poetic Edda. Gudrun had been married to the hero Sigurd and with him she had the daughter Svanhild. Svanhild had married the Gothic king Ermanaric (Jörmunrekkr), but betrayed him with the king's son, Randver. Furious Ermanaric hanged his own son and had Svanhild trampled to death by horses.
Gudrun wants to avenge her daughter and she agitates her sons Hamdir and Sörli, her sons with King Jonakr by telling them about her fate. They depart for their fateful vengeance, a story that is told in the Hamðismál, the last poem of the Poetic Edda.
References
Guðrúnarhvöt Wikipedia(Text) CC BY-SA