Joshua 4:5-7

5and Joshua said to them, Pass before the ark of Jehovah your 1God into the midst of the Jordan, and lift up each of you a stone [and put it] upon his shoulder, according to the number of the tribes of the children of Israel,

6that this may be a sign in your midst. When your children ask hereafter, saying, What mean ye by these stones?

7then ye shall say to them, That the waters of the Jordan were cut off before the ark of the covenant of Jehovah; when it went through 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.