Exodus 31:14-15

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].

15For six days work may be done, but the seventh is the Sabbath of complete rest, sacred to the Lord; whoever does work on the Sabbath day must be put to death.