Genesis 2:2-3 KJV

And on the seventh day God ended his work which he had made; and he rested on the seventh day from all his work which he had made. [3] And God blessed the seventh day, and sanctified it: because that in it he had rested from all his work which God created and made.

Exodus 31:15-16 KJV

Six days may work be done; but in the seventh is the sabbath of rest, holy to the LORD: whosoever doeth any work in the sabbath day, he shall surely be put to death. [16] Wherefore the children of Israel shall keep the sabbath, to observe the sabbath throughout their generations, for a perpetual covenant.