Numbers 10:8-10

8And the sons of Aaron, the priests, shall blow the trumpets. The trumpets shall be to you for a perpetual statute throughout your generations.

9And when you go to war in your land against the adversary who oppresses you, then you shall sound an alarm with the trumpets, that you may be remembered before the Lord your God, and you shall be saved from your enemies.

10On the day of your gladness also, and at your appointed feasts and at the beginnings of your months, you shall blow the trumpets over your burnt offerings and over the sacrifices of your peace offerings. They shall be a reminder of you before your God: I am the Lord your God."