Exodus 31:15 in the King James Version
Six days may work be done; but in the seventh is the sabbath of rest, holy to the LORD: whosoever doeth any work in the sabbath day, he shall surely be put to death.
Context
14 You 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 therein, that soul shall be cut off from among his people.
15 Six days shall work be done, but on the seventh day is a Sabbath of solemn rest, holy to the LORD. Whoever does any work on the Sabbath day shall surely be put to death.
16 Therefore the children of Israel shall keep the Sabbath, to observe the Sabbath throughout their generations, for a perpetual covenant.