Deuteronomy 27:5

And there shalt thou build an altar unto the Lord thy God, an altar of stones: thou shalt not lift up any iron tool upon them.

Cross-reference

Exodus 20:25 gives the same prohibition against iron tools on stone altars — the original commandment being repeated here.

Joshua 8:30 records Joshua building an altar on Mount Ebal — the direct fulfillment of this command.

Joshua 8:31 quotes the law of uncut stones and no iron tool — fulfilling this exact command for the altar.