Exodus 12:1-4 New Revised Standard Version (NRSV)
The First Passover Instituted
12 The Lord said to Moses and Aaron in the land of Egypt: 2 This month shall mark for you the beginning of months; it shall be the first month of the year for you. 3 Tell the whole congregation of Israel that on the tenth of this month they are to take a lamb for each family, a lamb for each household. 4 If a household is too small for a whole lamb, it shall join its closest neighbor in obtaining one; the lamb shall be divided in proportion to the number of people who eat of it.
Exodus 12:11-14 New Revised Standard Version (NRSV)
11 This is how you shall eat it: your loins girded, your sandals on your feet, and your staff in your hand; and you shall eat it hurriedly. It is the passover of the Lord. 12 For I will pass through the land of Egypt that night, and I will strike down every firstborn in the land of Egypt, both human beings and animals; on all the gods of Egypt I will execute judgments: I am the Lord. 13 The blood shall be a sign for you on the houses where you live: when I see the blood, I will pass over you, and no plague shall destroy you when I strike the land of Egypt.
14 This day shall be a day of remembrance for you. You shall celebrate it as a festival to the Lord; throughout your generations you shall observe it as a perpetual ordinance.