Numbers 10:7-9

Complete Jewish Bible

⁷ However, when the community is to be assembled, you are to sound; but don’t sound an alarm. ⁸ It will be the sons of Aharon, the cohanim, who are to sound the trumpets; this will be a permanent regulation for you through all your generations.

⁹ “When you go to war in your land against an adversary who is oppressing you, you are to sound an alarm with the trumpets; then you will be remembered before Adonai your God, and you will be saved from your enemies.