2 Samuel 18:21

Then said Joab to Cushi, Go tell the king what thou hast seen. And Cushi bowed himself unto Joab, and ran.

Joab chose Cushi as his messenger and charged him to go to the king and tell him what he had seen. Cushi was sent as the second runner with tidings from the battle, following the defeat of the rebellion. His report declared that the Lord had avenged David of all those who had risen up against him. That avenging work was made known in the news he bore that Absalom was dead.