From 18th century Icelandic manuscript of the Prose Edda.
"According to Skáldskaparmál, the gods Odin, Loki and Hœnir set out one day on a journey, traveling through mountains and wilderness until they were in need of food. In a valley they saw a herd of oxen, and they took one of the oxen and set it in an earth oven, but after a while they found that it would not cook. As they were trying to determine the reason for this, they heard someone talking in the oak tree above them, saying that he himself was the one responsible for the oven not cooking. They looked up and saw that it was Þjazi in the form of a great eagle, and he told them that if they would let him eat from the ox, then he would make the oven cook. To this they agreed, so he came down from the tree and began devouring a large portion of the meal. He ate so much of it that Loki became angry, grabbed his long staff and attempted to strike him, but the weapon stuck fast to Þjazi’s body and he took flight, carrying Loki up with him….”