Or HaChaim on Exodus 7:23/אור החיים על שמות ז׳:כ״ג

1 ויפן ..ולא שת לבו, He turned…and did not take due notice of this, etc. The Torah is careful not to write that Pharaoh expressly refused to let the Israelites depart; Pharaoh was very anxious not to expose himself to additional retribution. We will explain on 8,4, why Pharaoh had not asked Moses and Aaron in this case to pray on his behalf and to remove the plague.