Exodus 20:24-25

20:24 ‘You must make for me an altar made of earth, and you will sacrifice on it your burnt offerings and your peace offerings, your sheep and your cattle. In every place where I cause my name to be honored I will come to you and I will bless you. 20:25 If you make me an altar of stone, you must not build it of stones shaped with tools, for if you use your tool on it you have defiled it.

Exodus 24:4-5

24:4 and Moses wrote down all the words of the Lord. Early in the morning he built an altar at the foot of the mountain and arranged twelve standing stones – according to the twelve tribes of Israel. 24:5 He sent young Israelite men, and they offered burnt offerings and sacrificed young bulls for peace offerings to the Lord.