Numbers 10:1-9

The LORD spoke further to Moses, saying, “Make yourself two trumpets of silver, of hammered work you shall make them; and you shall use them for summoning the congregation and for having the camps set out. When both are blown, all the congregation shall gather themselves to you at the doorway of the tent of meeting. Yet if only one is blown, then the leaders, the heads of the divisions of Israel, shall assemble before you. But when you blow an alarm, the camps that are pitched on the east side shall set out. When you blow an alarm the second time, the camps that are pitched on the south side shall set out; an alarm is to be blown for them to set out. When convening the assembly, however, you shall blow without sounding an alarm. The priestly sons of Aaron, moreover, shall blow the trumpets; and this shall be for you a perpetual statute throughout your generations. When you go to war in your land against the adversary who attacks you, then you shall sound an alarm with the trumpets, that you may be remembered before the LORD your God, and be saved from your enemies.