Exodus 24:1-4

Then God said to Moses, “Come up to the LORD, you and Aaron, Nadab and Abihu (Aaron’s older sons), and seventy of Israel’s elders, and you shall worship at a [safe] distance. Moses alone shall approach the LORD, but the others shall not come near, nor shall the people come up with him.” Then Moses came and told the people everything that the LORD had said and all the ordinances. And all the people answered with one voice, “Everything the LORD has said we will do.” 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.