Exodus 31:13-15

Young's Literal Translation

¹³ `And thou, speak unto the sons of Israel, saying, Only, My sabbaths ye do keep, for it [is] a sign between Me and you, to your generations, to know that I, Jehovah, am sanctifying you;

¹⁴ and ye have kept the sabbath, for it [is] holy to you, he who is polluting it is certainly put to death -- for any who doeth work in it -- that person hath even been cut off from the midst of his people.

¹⁵ `Six days is work done, and in the seventh day [is] a sabbath of holy rest to Jehovah; any who doeth work in the sabbath-day is certainly put to death,