Genesis 4:8
6 Then the Lord said to Cain, “Why are you angry, and why is your expression downcast? 7 Is it not true that if you do what is right, you will be fine? But if you do not do what is right, sin is crouching at the door. It desires to dominate you, but you must subdue it.” 8 Cain spoke to his brother Abel.21 While they were in the field, Cain attacked his brother Abel and killed him.
2 Samuel 14:6
5 The king replied to her, “What do you want?” She answered, “I am a widow; my husband is dead. 6 Your servant has two sons. When the two of them got into a fight in the field, there was no one present who could intervene. One of them struck the other and killed him. 7 Now the entire family has risen up against your servant, saying, ‘Turn over the one who struck down his brother, so that we can execute him and avenge the death of his brother whom he killed. In so doing we will also destroy the heir.’ They want to extinguish my remaining coal, leaving no one on the face of the earth to carry on the name of my husband.”
Notes and References
"... And then, at yet another level, we find that such connections bind passages through the entire course of the narrative. Consider the matter of competition and violence between brothers. The story is about sibling rivalry, and especially about brother killing brother, from beginning to end. After all, it starts with Cain and Abel, and it ends with a story of King Solomon executing his half brother Adonijah! But sibling rivalry is not just a bookend, or even just a persistent theme. It is a connected, developed direction of the story. Thus, there is a classic riddle in the story of Cain and Abel: the text notes that Cain kills Abel when they are in the field. What is the significance of informing us that they are in a field at the time? Even early biblical commentators searched for the meaning of this seemingly inconsequential detail. But in the story of King David’s rivalrous sons, we have the story of another fratricide: Absalom has his half brother Amnon killed (for raping Tamar). In an attempt to get David to pardon Absalom, a woman known as the “wise woman of Tekoa” comes and tells a story to David. She says that one of her two sons killed the other. In the course of her account, she mentions a seemingly unrelated detail: they fought “in the field” (2 Samuel 14:6). The appearance of the same extraneous detail in both stories of brother killing brother does not seem accidental, especially in light of all the other evidence indicating that these two stories belong to a single author’s work ..."
Friedman, Richard Elliott The Hidden Book in the Bible (p. 42) Harper San Francisco, 1998