וַיַּכְבֵּ֤ד פַּרְעֹה֙ אֶת־לִבּ֔וֹ גַּ֖ם בַּפַּ֣עַם הַזֹּ֑את וְלֹ֥א שִׁלַּ֖ח אֶת־הָעָֽם׃ (פ)
And Pharaoh hardened his heart this time also, and he did not let the people go.
Read midrashic interpretation of Exodus 8:28: and classical rabbinic exegesis.