Ezekiel 20:12, 20-21

Also I gave them My Sabbaths to be a sign between Me and them, that they might know [without any doubt] that I am the LORD who sanctifies them (separates and sets them apart).

Sanctify My Sabbaths and keep them holy; and they shall be a sign between Me and you, that you may know [without any doubt] that I am the LORD your God.’ Yet the children rebelled against Me; they did not walk in My statutes, nor were they careful to observe My ordinances, which, if a man keeps, he will live; they profaned My Sabbaths. Then I decided to pour out My wrath on them and finish My anger against them in the wilderness.