Exodus 12:1-4; Exodus 12:11-14
The LORD said to Moses and Aaron in Egypt,
"This month is to be for you the first month, the first month of your year.
Tell the whole community of Israel that on the tenth day of this month each man is to take a lamb for his family, one for each household.
If any household is too small for a whole lamb, they must share one with their nearest neighbor, having taken into account the number of people there are. You are to determine the amount of lamb needed in accordance with what each person will eat.
This is how you are to eat it: with your cloak tucked into your belt, your sandals on your feet and your staff in your hand. Eat it in haste; it is the LORD's Passover.
"On that same night I will pass through Egypt and strike down every firstborn--both men 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.