Numbers 10:6-8

American Standard Version

⁶ And when ye blow an alarm the second time, the camps that lie on the south side shall take their journey: they shall blow an alarm for their journeys. 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.