Exodus 20:24-25

24An altar of earth thou shalt make to me, and shalt sacrifice on it thy burnt offerings, and thy peace offerings, thy sheep, and thy oxen: in all places where I record my name I will come to thee, and I will bless thee. 25And if thou wilt make me an altar of stone, thou shalt not build it of hewn stone: for if thou shalt lift up thy tool upon it, thou hast polluted it.1