Joshua 3:2-4

At the end of three days the officers went through the camp and commanded the people, “As soon as you see the ark of the covenant of the LORD your God being carried by the Levitical priests, then you shall set out from your place and follow it. Yet there shall be a distance between you and it, about 2,000 cubits in length. Do not come near it, in order that you may know the way you shall go, for you have not passed this way before.”