Joshua 4:5-7

5and Joshua said unto them, Pass over before the ark of Jehovah your God into the midst of the Jordan, and take you up every man of you a stone upon his shoulder, according unto the number of the tribes of the children of Israel; 6that this may be a sign among you, that, when your children ask in time to come, saying, What mean ye by these stones? 7then ye shall say unto them, Because the waters of the Jordan were cut off before the ark of the covenant of Jehovah; when it passed over the Jordan, the waters of the Jordan were cut off: and these stones shall be for a memorial unto the children of Israel for ever.