Exodus 12:12-14 NIV
“On that same night I will pass through Egypt and strike down every firstborn of both people and animals, and I will bring judgment on all the gods of Egypt. I am the LORD. The blood will be a sign for you on the houses where you are, and when I see the blood, I will pass over you. No destructive plague will touch you when I strike Egypt.
“This is a day you are to commemorate; for the generations to come you shall celebrate it as a festival to the LORD—a lasting ordinance.
NIV: New International Version