Numbers 10:9-10

⁹When you go to war in your land against an adversary who oppresses you, then you must sound an alarm with the trumpets. I, Yahweh your God, will call you to mind and save you from your enemies.

¹⁰Also, at the times of celebration, both your regular festivals and at the beginnings of the months, you must blow the trumpets over your burnt offerings and over the sacrifices for your fellowship offerings. These will act as a reminder of you to me, your God. I am Yahweh your God.”