Numbers 10:8-10

⁸And the sons of Aaron, the priests, shall blow the trumpets; and they shall be to you for a statute for ever throughout your generations. ⁹And when ye go to war in your land against the adversary that oppresseth you, then ye shall sound an alarm with the trumpets; and ye shall be remembered before Jehovah your God, and ye shall be saved from your enemies. ¹⁰Also in the day of your gladness, and in your set feasts, and in the beginnings of your months, ye shall blow the trumpets over your burnt-offerings, and over the sacrifices of your peace-offerings; and they shall be to you for a memorial before your God: I am Jehovah your God.