Exodus 10:27 Midrash

וַיְחַזֵּ֥ק יְהוָ֖ה אֶת־לֵ֣ב פַּרְעֹ֑ה וְלֹ֥א אָבָ֖ה לְשַׁלְּחָֽם׃

But the LORD hardened Pharaoh’s heart, and he would not let them go.

Read midrashic interpretation of Exodus 10:27: and classical rabbinic exegesis.