Exodus 31:13-14

13And thou, speak thou unto the children of Israel, saying, Surely my sabbaths shall ye keep; for this is a sign between me and you throughout your generations, that ye may know that it is I, Jehovah, who do hallow you.

14Keep the sabbath, therefore; for it is holy unto you; every one that profaneth it shall certainly be put to death: yea, whoever doeth work on it, that soul shall be cut off from among his peoples.