Exodus 31:14
14 You shall keep the Sabbath, because it is holy for you. Everyone who profanes it shall be put to death. nWhoever does any work on it, that soul shall be cut off from among his people.
Exodus 35:2
2 cSix days work shall be done, but on the seventh day you shall have a Sabbath of solemn rest, holy to the Lord. Whoever does any work on it shall be put to death.