Numbers 10:7-9

King James Version

⁷ But when the congregation 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 with the trumpets; and they shall be to you for an ordinance for ever throughout your generations.

⁹ And if ye go to war in your land against the enemy that oppresseth you, then ye shall blow an alarm with the trumpets; and ye shall be remembered before the Lord your God, and ye shall be saved from your enemies.