2 Samuel 18:16

And Joab blew the trumpet, and the people returned from pursuing after Israel: for Joab held back the people.

Cross-reference

In 2 Samuel 2:28, Joab similarly blows a trumpet to stop the pursuit after a rebel leader's death.

In 2 Samuel 20:22, Joab again blows a trumpet to disperse the city after Sheba's death.

Numbers 10:2–10 Historical context

Numbers 10:2-10 gives the law for silver trumpets to signal assemblies and war, establishing the practice Joab follows.