Exodus 24:4, 7

Moses wrote down all the words of the LORD. Then he got up early in the morning, and built an altar [for worship] at the foot of the mountain with twelve pillars (memorial stones) representing the twelve tribes of Israel.

Then he took the Book of the Covenant and read it aloud to the people; and they said, “Everything that the LORD has said we will do, and we will be obedient.”