Exodus 24:3-5

3When Moses went and told the people all the Lord’s words and laws, they responded with one voice, “Everything the Lord has said we will do.”

4Moses then wrote down everything the Lord had said. He got up early the next morning and built an altar at the foot of the mountain and set up twelve stone pillars representing the twelve tribes of Israel.

5Then he sent young Israelite men, and they offered burnt offerings and sacrificed young bulls as fellowship offerings to the Lord.