Deuteronomy 27:4-7

Now when you cross the Jordan you shall set up these stones on Mount Ebal, just as I am commanding you today and coat them with plaster. There you shall build an altar to the LORD your God, an altar of stones; you shall not use an iron tool on them. You shall build the altar of the LORD your God with whole [uncut] stones, and offer burnt offerings on it to the LORD your God; and you shall sacrifice peace offerings and shall eat there, and shall rejoice before the LORD your God.