Joshua 4:4-7

Then Joshua called the twelve men from the people of Israel, whom he had appointed, a man from each tribe. And Joshua said to them, “Pass on before the ark of the LORD your God into the midst of the Jordan, and take up each of you a stone upon his shoulder, according to the number of the tribes of the people of Israel, that this may be a sign among you. When your children ask in time to come, ‘What do those stones mean to you?’ then you shall tell them that the waters of the Jordan were cut off before the ark of the covenant of the LORD. When it passed over the Jordan, the waters of the Jordan were cut off. So these stones shall be to the people of Israel a memorial forever.”