Deuteronomy 27:4-7

4Now 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.

5There you shall build an altar to the Lord your God, an altar of stones; you shall not use an iron tool on them.

6You shall build the altar of the Lord your God with whole [uncut] stones, and offer burnt offerings on it to the Lord your God;

7and you shall sacrifice peace offerings and shall eat there, and shall rejoice before the Lord your God.