Exodus 12:3-4

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: {lamb: or, kid} 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.