Exodus 31:14-15

14The Sabbath day must be special for you, because it is a holy day. If anyone does not make the Sabbath a special day, you must punish him with death. If anyone does any work on a Sabbath day, he can no longer belong to my people.

15You may work for six days each week, but the seventh day is a day of rest. It is a holy day that is special to me, the Lord. If anyone does any work on a Sabbath day, you must punish him with death.