Numbers 10:7-9

Darby Translation

⁷ And when the congregation is to be gathered together, ye shall blow, but ye shall not blow an alarm:

⁸ the sons of Aaron, the priests, shall blow with the trumpets; and they shall be to you for an everlasting statute 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 Jehovah your God, and ye shall be saved from your enemies.