Exodus 32:15-16

32:15 Moses turned and went down from the mountain with the two tablets of the testimony in his hands. The tablets were written on both sides – they were written on the front and on the back. 32:16 Now the tablets were the work of God, and the writing was the writing of God, engraved on the tablets.

Exodus 32:19

32:19 When he approached the camp and saw the calf and the dancing, Moses became extremely angry. He threw the tablets from his hands and broke them to pieces at the bottom of the mountain.