Exodus 31:14-16

14You shall keep the Sabbath, therefore, for it is holy to you. Everyone who profanes it shall surely be put to death; for whoever does any work on it, that person shall be cut off from among his people.

15Work shall be done for six days, but the seventh is the Sabbath of rest, holy to the Lord. Whoever does any work on the Sabbath day, he shall surely be put to death.

16Therefore the children of Israel shall keep the Sabbath, to observe the Sabbath throughout their generations as a perpetual covenant.