וַיִּקְרָ֣א פַרְעֹ֔ה אֶל־מֹשֶׁ֖ה וּֽלְאַהֲרֹ֑ן וַיֹּ֗אמֶר לְכ֛וּ זִבְח֥וּ לֵֽאלֹהֵיכֶ֖ם בָּאָֽרֶץ׃
And Pharaoh called for Moses and for Aaron, and said: ‘Go ye, sacrifice to your God in the land.’
Read midrashic interpretation of Exodus 8:21: and classical rabbinic exegesis.