Exodus 31:13-14

13“But as for you, say to the Israelites, ‘You shall most certainly observe My Sabbaths, for it is a sign between Me and you throughout your generations, so that you may know [without any doubt] and acknowledge that I am the Lord who sanctifies you and sets you apart [for Myself].

14Therefore, you shall keep the Sabbath, for it is holy to you. Everyone who profanes it must be put to death; for whoever does work on the Sabbath, that person (soul) shall be cut off from among his people [excluding him from the atonement made for them].