Exodus 31:13-17 (NKJV)
13 "Speak also to the children of Israel, saying: ‘Surely My Sabbaths you shall keep, for it is a sign between Me and you throughout your generations, that you may know that I am the LORD who sanctifies you."
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 on it, that person shall be cut off from among his people."
15 "‘Work 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."
16 "‘Therefore the children of Israel shall keep the Sabbath, to observe the Sabbath throughout their generations as a perpetual covenant."
17 "‘It is a sign between Me and the children of Israel forever; for in six days the LORD made the heavens and the earth, and on the seventh day He rested and was refreshed.’"