Joshua 4:5-7

and Joshua said to them, “Cross again to the ark of the LORD your God into the middle of the Jordan, and each of you take up a stone on his shoulder, according to the number of the tribes of the sons of Israel. Let this be a sign among you, so that when your children ask later, saying, ‘What do these stones mean to you?’ then you shall say to them, ‘Because the waters of the Jordan were cut off before the ark of the covenant of the LORD; when it crossed the Jordan, the waters of the Jordan were cut off.’ So these stones shall become a memorial to the sons of Israel forever.”