Exodus 20:24-25

24Instead, use earth to make an altar for me. You must offer sacrifices to me on the altar. You may take your sheep, your goats or your cows to make burnt offerings or friendship offerings or other sacrifices to me. Make an altar like this in any place that I choose for you to worship me. In those places, I will come to you and I will bless you.

25You may also use stones from the ground to make an altar for me. But do not use any tools to cut the stones. If you use a tool on the stones, the altar will not be right for you to worship me there.