Exodus 31:15-18

31:15 Six days work may be done, but on the seventh day is a Sabbath of complete rest, holy to the Lord; anyone who does work on the Sabbath day must surely be put to death. 31:16 The Israelites must keep the Sabbath by observing the Sabbath throughout their generations as a perpetual covenant. 31:17 It is a sign between me and the Israelites forever; for in six days the Lord made the heavens and the earth, and on the seventh day he rested and was refreshed.’”

31:18 He gave Moses two tablets of testimony when he had finished speaking with him on Mount Sinai, tablets of stone written by the finger of God.