Joshua 3:2-4

And it came to pass after three days, that the officers went through the midst of the camp; and they commanded the people, saying, When ye see the ark of the covenant of Jehovah your God, and the priests the Levites bearing it, then ye shall remove from your place, and go after it. Yet there shall be a space between you and it, about two thousand cubits by measure: come not near unto it, that ye may know the way by which ye must go; for ye have not passed this way heretofore.