Joshua 4:5-7

5And Joshua said unto them, Pass over before the ark of Yhwh 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:

6That 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?1

7Then ye shall answer them, That the waters of Jordan were cut off before the ark of the covenant of Yhwh; 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.