Numbers 10:2-8

2“Make two silver trumpets for yourself; you shall make them of hammered work; you shall use them for calling the congregation and for directing the movement of the camps.

3When they blow both of them, all the congregation shall gather before you at the door of the tabernacle of meeting.

4But if they blow only one, then the leaders, the heads of the divisions of Israel, shall gather to you.

5When you sound the advance, the camps that lie on the east side shall then begin their journey.

6When you sound the advance the second time, then the camps that lie on the south side shall begin their journey; they shall sound the call for them to begin their journeys.

7And when the assembly is to be gathered together, you shall blow, but not sound the advance.

8The sons of Aaron, the priests, shall blow the trumpets; and these shall be to you as an ordinance forever throughout your generations.