Exodus 20:22-26 - Instructions For Building Altars
22 And LORD said to Moses, Thus thou shall say to the sons of Israel, Ye yourselves have seen that I have talked with you from heaven. 23 Ye shall not make [other gods] with me; gods of silver, or gods of gold, ye shall not make to you.
24 An altar of earth thou shall make to me, and shall sacrifice on it thy burnt-offerings, and thy peace-offerings, thy sheep, and thine oxen. In every place where I record my name I will come to thee and I will bless thee. 25 And if thou make to me an altar of stone, thou shall not build it of hewn stones, for if thou lift up thy tool upon it, thou have polluted it. 26 Neither shall thou go up by steps to my altar, that thy nakedness be not uncovered on it.