Shemoth (Exodus) 31:16-17

‘And the children of Yisra’ĕl shall guard the Sabbath, to perform the Sabbath throughout their generations as an everlasting covenant. ‘Between Me and the children of Yisra’ĕl it is a sign forever. For in six days יהוה made the heavens and the earth, and on the seventh day He rested and was refreshed.’ ”