Exodus 31:12-14

And Jehovah spake unto Moses, saying, Speak thou also unto the children of Israel, saying, Verily ye shall keep my sabbaths: for it is a sign between me and you throughout your generations; that ye may know that I am Jehovah who sanctifieth you. 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.