Exodus 20:22-26 - Instructions For Building Altars
22 And the Lord said to Moses, Say to the children of Israel, You yourselves have seen that my voice has come to you from heaven 23 Gods of silver and gods of gold you are not to make for yourselves.
24 Make for me an altar of earth, offering on it your burned offerings and your peace-offerings, your sheep and your oxen: in every place where I have put the memory of my name, I will come to you and give you my blessing. 25 And if you make me an altar of stone do not make it of cut stones: for the touch of an instrument will make it unclean. 26 And do not go up by steps to my altar, for fear that your bodies may be seen uncovered.