Numbers 10:8-9

Context10:8 The sons of Aaron, the priests, must blow the trumpets; and they will be to you for an eternal ordinance throughout your generations. 10:9 If you go to war in your land against an adversary who opposes 1 you, then you must sound an alarm with the trumpets, and you will be remembered before the Lord your God, and you will be saved 2 from your enemies.