Joshua 4:5-7

5Joshua said to them, “Cross over before the ark of Adonai your God into the middle of the Jordan. Each of you, lift up a stone on his shoulder, for the number of the tribes of Bnei-Yisrael.

6Let this be a sign among you. When your children ask later saying, ‘What do these stones mean to you?’

7then you will say to them: ‘Because the waters of the Jordan were cut off before the ark of the covenant of Adonai—when it crossed the Jordan—the waters of the Jordan were cut off.’ So these stones will be a reminder to Bnei-Yisrael forever.”