Exodus 20:24-26

An altar of earth you shall make for me and sacrifice on it your burnt offerings and your peace offerings, your sheep and your oxen. In every place where I cause my name to be remembered I will come to you and bless you. If you make me an altar of stone, you shall not build it of hewn stones, for if you wield your tool on it you profane it. And you shall not go up by steps to my altar, that your nakedness be not exposed on it.’