Exodus 24:4

24:4 and Moses wrote down all the words of the Lord. Early in the morning he built an altar at the foot of the mountain and arranged twelve standing stones – according to the twelve tribes of Israel.

Exodus 34:28

34:28 So he was there with the Lord forty days and forty nights; he did not eat bread, and he did not drink water. He wrote on the tablets the words of the covenant, the ten commandments.