Rashi on Exodus 8:11/רש"י על שמות ח׳:י״א

1והכבד את לבו HE ALLOWED HIS HEART TO BE HARDENED — The word הַכְבֵּד expresses doing something (the Hebrew infinitive but having a past meaning) just as, (Genesis 12:9) “going (הלוך) and journeying (ונסוע)”. So, too, (2 Kings 3:24) “and smiting (והכת) Moab”; (I Samuel 22:13) “and enquiring (ושאול) of God for him”; (1 Kings 20:37); “smiting (הכה) and wounding (ופצוע)”.

2‎ כאשר דבר ה׳ AS THE LORD HAD SPOKEN — And where had He said this? When He said, (Exodus 7:4) “Pharaoh will not hearken to you”.