Joshua 4:4-7

Then Joshua called the twelve men, whom he had prepared of the children of Israel, out of every tribe a man: And Joshua said unto them, Pass over before the ark of the LORD your God into the midst of Jordan, and take ye up every man of you a stone upon his shoulder, according unto the number of the tribes of the children of Israel: That this may be a sign among you, {that} when your children ask {their fathers} in time to come, saying, What {mean} ye by these stones? {in time...: Heb. to morrow} Then ye shall answer them, That the waters of Jordan were cut off before the ark of the covenant of the LORD; when it passed over Jordan, the waters of Jordan were cut off: and these stones shall be for a memorial unto the children of Israel for ever.