Deuteronomy 27:6

4It shall be, when you have crossed over the Jordan, that you shall set up these stones, which I command you today, on Mount Ebal, and you shall coat them with plaster.

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

6You shall build the LORD your God’s altar of uncut stones. You shall offer burnt offerings on it to the LORD your God.

7You shall sacrifice peace offerings, and shall eat there. You shall rejoice before the LORD your God.

8You shall write on the stones all the words of this law very plainly.”