Exod 12:3-5

3Tell 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.4If 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.5Your lamb shall be without blemish, a year-old male; you may take it from the sheep or from the goats.