Deuteronomy 16:1

Keep the passover - A feast so called because the angel that destroyed the firstborn of the Egyptians, seeing the blood of the appointed sacrifice sprinkled on the lintels and door-posts of the Israelites' houses, passed over Them, and did not destroy any of their firstborn. See the notes on Exodus 12:2 , and Exodus 12:3 ; (note), etc.