Exodus 31:12-15

12And Yhwh spake unto Moses, saying, 13Speak thou also unto the children of Israel, saying, Verily my sabbaths ye shall keep: for it is a sign between me and you throughout your generations; that ye may know that I am Yhwh that doth sanctify you. 14Ye shall keep the sabbath therefore; for it is holy unto you: every one that defileth it shall surely be put to death: for whosoever doeth any work therein, that soul shall be cut off from among his people. 15Six days may work be done; but in the seventh is the sabbath of rest, holy to Yhwh: whosoever doeth any work in the sabbath day, he shall surely be put to death.1