Exodus 12:1-4 (KJV)

1 And the LORD spake unto Moses and Aaron in the land of Egypt, saying,

2 This month shall be unto you the beginning of months: it shall be the first month of the year to you.

3 Speak ye unto all the congregation of Israel, saying, In the tenth day of this month they shall take to them every man a lamb, according to the house of their fathers, a lamb for an house:

4 And if the household be too little for the lamb, let him and his neighbour next unto his house take it according to the number of the souls; every man according to his eating shall make your count for the lamb.