Ex 31:12-13 Yahweh spoke to Moses, saying, “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 Yahweh who sanctifies you.
Ex 31:16-18 Therefore the children of Israel shall keep the Sabbath, to observe the Sabbath throughout their generations as a perpetual covenant. It is a sign between Me and the children of Israel forever; for in six days the Yahweh made the heavens and the earth, and on the seventh day He rested and was refreshed.'”
When He had made an end of speaking with him on Mount Sinai, He gave Moses two tablets of the Testimony, tablets of stone, written with the finger of (Yahweh) God.