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.