Numbers 10:1-9

And the LORD spoke to Moses, saying: “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. When they blow both of them, all the congregation shall gather before you at the door of the tabernacle of meeting. But if they blow only one, then the leaders, the heads of the divisions of Israel, shall gather to you. When you sound the advance, the camps that lie on the east side shall then begin their journey. When 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. And when the assembly is to be gathered together, you shall blow, but not sound the advance. The sons of Aaron, the priests, shall blow the trumpets; and these shall be to you as an ordinance forever throughout your generations. “When you go to war in your land against the enemy who oppresses you, then you shall sound an alarm with the trumpets, and you will be remembered before the LORD your God, and you will be saved from your enemies.