The LORD then gave these further instructions to Moses:
"Tell the people of Israel to keep my Sabbath day, for the Sabbath is a sign of the covenant between me and you forever. It helps you to remember that I am the LORD, who makes you holy.
Yes, keep the Sabbath day, for it is holy. Anyone who desecrates it must die; anyone who works on that day will be cut off from the community.
Work six days only, but the seventh day must be a day of total rest. I repeat: Because the LORD considers it a holy day, anyone who works on the Sabbath must be put to death.
The people of Israel must keep the Sabbath day forever.
It is a permanent sign of my covenant with them. For in six days the LORD made heaven and earth, but he rested on the seventh day and was refreshed."
Then as the LORD finished speaking with Moses on Mount Sinai, he gave him the two stone tablets inscribed with the terms of the covenant, written by the finger of God.
References for Exodus 31:18