Exodus 31:13

31:13 “Tell the Israelites, ‘Surely you must keep my Sabbaths, for it is a sign between me and you throughout your generations, that you may know that I am the Lord who sanctifies you.

Exodus 31:17

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.’”