וַיֹּ֨אמֶר יְהוָ֜ה אֶל־מֹשֶׁ֗ה דַּבֵּר֮ אֶל־אַהֲרֹ֣ן אָחִיךָ֒ וְאַל־יָבֹ֤א בְכָל־עֵת֙ אֶל־הַקֹּ֔דֶשׁ מִבֵּ֖ית לַפָּרֹ֑כֶת אֶל־פְּנֵ֨י הַכַּפֹּ֜רֶת אֲשֶׁ֤ר עַל־הָאָרֹן֙ וְלֹ֣א יָמ֔וּת כִּ֚י בֶּֽעָנָ֔ן אֵרָאֶ֖ה עַל־הַכַּפֹּֽרֶת׃
Targum Jonathan on Leviticus
And the Lord said unto Mosheh: Speak with Aharon thy brother, that he enter not at any time into the holy place within the veil before the mercy-seat; for the cloud of the glory of My Shekinah is revealed over the place of the mercy-seat.