Numbers 10:4-7

But if they blow only one, then the chiefs, the heads of the tribes of Israel, shall gather themselves to you. When you blow an alarm, the camps that are on the east side shall set out. And when you blow an alarm the second time, the camps that are on the south side shall set out. An alarm is to be blown whenever they are to set out. But when the assembly is to be gathered together, you shall blow a long blast, but you shall not sound an alarm.