Numbers 10:7-9

American Standard Version

⁷ But when the assembly is to be gathered together, ye shall blow, but ye shall not sound an alarm. ⁸ And the sons of Aaron, the priests, shall blow the trumpets; and they shall be to you for a statute for ever throughout your generations. ⁹ And 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.