Numbers 10:8-10

8The sons of Aaron, the priests, are to sound the trumpets. Your use of these is a permanent statute throughout your generations.

9“When you enter into battle in your land against an adversary who is attacking you, sound short blasts on the trumpets, and you will be remembered before the Lord your God and be saved from your enemies.

10You are to sound the trumpets over your burnt offerings and your fellowship sacrifices and on your joyous occasions, your appointed festivals, and the beginning of each of your months. They will serve as a reminder for you before your God: I am the Lord your God.”