Exodus 31:14-15

Ye shall keep the sabbath therefore; for it is holy unto you: every one that profaneth it shall surely be put to death; for whosoever doeth any work therein, that soul shall be cut off from among his people. Six days shall work be done, but on the seventh day is a sabbath of solemn rest, holy to Jehovah: whosoever doeth any work on the sabbath day, he shall surely be put to death.