Numbers 10:7-10

7And when the assembly is to be gathered together, you shall blow, but not sound the advance.

8The sons of Aaron, the priests, shall blow the trumpets; and these shall be to you as an ordinance forever throughout your generations.

9“When you go to war in your land against the enemy who oppresses you, then you shall sound an alarm with the trumpets, and you will be remembered before the Lord your God, and you will be saved from your enemies.

10Also in the day of your gladness, in your appointed feasts, and at the beginning of your months, you shall blow the trumpets over your burnt offerings and over the sacrifices of your peace offerings; and they shall be a memorial for you before your God: I am the Lord your God.”