Numbers 10:4-8

And if they blow but with one trumpet, then the princes, which are heads of the thousands of Israel, shall gather themselves unto thee.

When ye blow an alarm, then the camps that lie on the east parts shall go forward.

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

But when the congregation is to be gathered together, ye shall blow, but ye shall not sound an alarm.

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.