Exodus 31:13-14

31:13 “Tell the Israelites, ‘Surely you must keep my Sabbaths, for it is a sign between me and you throughout your generations, that you may know that I am the Lord who sanctifies you. 31:14 So you must keep the Sabbath, for it is holy for you. Everyone who defiles it must surely be put to death; indeed, if anyone does any work on it, then that person will be cut off from among his people.