Exodus 20:24-25

24An altar of earth you shall make for Me, and you shall sacrifice on it your burnt offerings and your peace offerings, your sheep and your oxen. In every place where I record My name I will come to you, and I will bless you.

25And if you make Me an altar of stone, you shall not build it of hewn stone; for if you use your tool on it, you have profaned it.