Joshua 4:6-8

⁶This shall be a sign among you; when your children ask later, saying, ‘What do these stones mean to you?’ ⁷then you shall say to them, ‘That 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.”

⁸So the sons of Israel did exactly as Joshua commanded, and took up twelve stones from the middle of the Jordan, just as the Lord spoke to Joshua, according to the number of the tribes of the sons of Israel; and they carried them over with them to the encampment and put them down there.