Exodus 24:3-5

3And Moses came and told the people all the words of Yhwh, and all the judgments: and all the people answered with one voice, and said, All the words which Yhwh hath said will we do. 4And Moses wrote all the words of Yhwh, and rose up early in the morning, and builded an altar under the hill, and twelve pillars, according to the twelve tribes of Israel. 5And he sent young men of the children of Israel, which offered burnt offerings, and sacrificed peace offerings of oxen unto Yhwh.