וְגַ֤ם אֶת־שַׁבְּתוֹתַי֙ נָתַ֣תִּי לָהֶ֔ם לִהְי֣וֹת לְא֔וֹת בֵּינִ֖י וּבֵֽינֵיהֶ֑ם לָדַ֕עַת כִּ֛י אֲנִ֥י יְהוָ֖ה מְקַדְּשָֽׁם׃
Moreover also I gave them My sabbaths, to be a sign between Me and them, that they might know that I am the LORD that sanctify them.
Read midrashic interpretation of Ezekiel 20:12: and classical rabbinic exegesis.