Numbers 10:7-9

Amplified Bible

⁷ When the assembly is to be gathered, you shall blow [the trumpets in short, sharp tones], but without sounding an alarm. ⁸ The sons of Aaron, the priests, shall blow the trumpets; and the trumpets shall be for you a perpetual statute throughout your generations. ⁹ When you go to war in your land against the enemy that attacks you, then sound an alarm with the trumpets, so that you may be remembered before the Lord your God, and you shall be saved from your enemies.