exodus 12:29 And it came to pass, that at midnight the LORD smote all the firstborn in the land of Egypt, from the firstborn of Pharaoh that sat on his throne unto the firstborn of the captive that was in the dungeon; and all the firstborn of cattle. - Free Bible Online

      29. at midnight the Lord smote all the first-born in the land of Egypt--At the moment when the Israelites were observing the newly instituted feast in the singular manner described, the threatened calamity overtook the Egyptians. It is more easy to imagine than describe the confusion and terror of that people suddenly roused from sleep and enveloped in darkness--none could assist their neighbors when the groans of the dying and the wild shrieks of mourners were heard everywhere around. The hope of every family was destroyed at a stroke. This judgment, terrible though it was, evinced the equity of divine retribution. For eighty years the Egyptians had caused the male children of the Israelites to be cast into the river [Ex 1:16], and now all their own first-born fell under the stroke of the destroying angel. They were made, in the justice of God, to feel something of what they had made His people feel. Many a time have the hands of sinners made the snares in which they have themselves been entangled, and fallen into the pit which they have dug for the righteous [Pr 28:10]. "Verily there is a God that judgeth in the earth" [Ps 58:11].

JFB.