2 Samuel 2:18
And there were three sons of Zeruiah there, Joab, and Abishai, and Asahel: and Asahel was as light of foot as a wild roe. And there were three sons of Zeruiah there, Joab, and Abishai, and Asahel: and Asahel was as light of foot as a wild roe.
The naming places Asahel alongside his brothers Joab and Abishai as sons of Zeruiah at the time of open war between Israel and Judah. That conflict is the setting recorded in 2 Samuel 2:18-23, where the forces of the two kingdoms met in battle. In the course of that fighting Abner struck down Asahel, who was Joab's brother. Asahel's death at Abner's hand afterward became the ground of Joab's blood-feud against Abner and led Joab to murder him in revenge.