2 Samuel 3:30

So Joab and Abishai his brother killed Abner because he had put their brother Asahel to death in the battle at Gibeon.

2 Samuel 2:19-23

Asahel pursued Abner and did not turn to the right or to the left from following Abner.

Proverbs 28:17

A man who is laden with the guilt of human blood
Will be a fugitive until death; let no one support him.

Acts 28:4

When the natives saw the creature hanging from his hand, they began saying to one another, “Undoubtedly this man is a murderer, and though he has been saved from the sea, justice has not allowed him to live.”

Treasury of Scripture Knowledge

Summary

So Joab and Abishai his brother slew Abner, because he had slain their brother Asahel at Gibeon in the battle.

Because

Bible References

Slew abner

Proverbs 28:17
A man who is laden with the guilt of human blood
Will be a fugitive until death; let no one support him.
Acts 28:4
When the natives saw the creature hanging from his hand, they began saying to one another, “Undoubtedly this man is a murderer, and though he has been saved from the sea, justice has not allowed him to live.”

Because

2 Samuel 2:19
Asahel pursued Abner and did not turn to the right or to the left from following Abner.