Exodus 24:3-5

3Moses came and told the people all the words of the Lord and all the rules. And all the people answered with one voice and said, "All the words that the Lord has spoken we will do."

4And Moses wrote down all the words of the Lord. He rose early in the morning and built an altar at the foot of the mountain, and twelve pillars, according to the twelve tribes of Israel.

5And he sent young men of the people of Israel, who offered burnt offerings and sacrificed peace offerings of oxen to the Lord.