Exodus 12:3, 6-7, 12-13

Tell all the congregation of Israel that on the tenth day of this month every man shall take a lamb according to their fathers’ houses, a lamb for a household.

and you shall keep it until the fourteenth day of this month, when the whole assembly of the congregation of Israel shall kill their lambs at twilight. “Then they shall take some of the blood and put it on the two doorposts and the lintel of the houses in which they eat it.

For I will pass through the land of Egypt that night, and I will strike all the firstborn in the land of Egypt, both man and beast; and on all the gods of Egypt I will execute judgments: I am the LORD. The blood shall be a sign for you, on the houses where you are. And when I see the blood, I will pass over you, and no plague will befall you to destroy you, when I strike the land of Egypt.