Exodus 31:15 - 31:17
15 Six days work may be done, but on the seventh day there is a sabbath of complete rest, holy to Yahweh; whoever does any work on the sabbath day shall surely be put to death. 16 So the sons of Israel shall keep the sabbath, to celebrate the sabbath throughout their generations as an everlasting covenant.’ 17 It is a sign between Me and the sons of Israel forever; for in six days Yahweh made heaven and earth, but on the seventh day He rested and was refreshed.”